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  • Biochemistry and Biotechnology  (879)
  • Inorganic Chemistry  (608)
  • 1995-1999  (1,487)
  • 1990-1994
  • 1950-1954
  • 1997  (1,487)
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  • 1995-1999  (1,487)
  • 1990-1994
  • 1950-1954
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  • 101
    Electronic Resource
    Electronic Resource
    A Kalman filter algorithm and monitoring apparatus for at-line control of fractional protein precipitation (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 58-70 
    Details
    ISSN: 0006-3592
    Keywords: control ; monitoring ; fractional precipitation ; protein ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Downstream processing operations are often carried out blind in the process timescale since product monitoring on-line is not common. Knowledge of the location and concentration of the product and key contaminants is complementary to other process information for process development and, if available on-line in conjunction with a suitable model, control. This article sets out to demonstrate a model describing a two-cut fractional protein precipitation process and how this may be used for control of the process to maximize yield in the face of variable process stream conditions. Estimation of the model parameters is achieved by means of data-fitting by least squares and in comparison prediction by a Kalman filter algorithm. A description and error analysis of equipment for at-line monitoring of the soluble product in a pilot plant environment is presented which includes a micro-centrifuge necessary to clarify small volumes of sample prior to analysis. Finally, an account of the successful implementation of this equipment and the Kalman filter algorithm for control at bench scale is given where conditions in the process stream are deliberately disturbed to test the control operation. © 1997 John Wiley & Sons, Inc.
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  • 102
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    Preparation of magnetically susceptible polyacrylamide/magnetite beads for use in magnetically stabilized fluidized bed chromatography (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 79-87 
    Details
    ISSN: 0006-3592
    Keywords: polyacrylamide ; magnetic ; stabilized ; fluidized bed ; chromatography ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Spherical polyacrylamide/magnetite (PAM) composite beads, suitable for use in a magnetically stabilized fluidized bed (MSFB), were manufactured by a suspension polymerization method. Yield of beads depended on the type and concentration of buffer used during polymerization as well as the pH. More stabilizer was needed to prevent bead agglomeration as magnetite concentration increased. Bead diameter ranged from less than 60 to 600 μm, depending on reaction conditions, and the bead mean diameter and size distribution decreased with increasing impeller speed. The density and roundness factor of the beads were 1.19 ± 0.02 g cm-3 and 1.08 ± 0.03, respectively. The beads had high magnetization at a low applied magnetic field strength (60 mT at 75 kA m-1) and retained little residual magnetization (〈2 mT) after the field was removed. Incorporation of magnetite did not significantly affect the physical strength of the beads: the beads' average elastic modulus was 14 ± 4 kPa, similar to reported values for polyacrylamide gels (15.8 kPa). The beads were stable in a range of buffers from pH 1 to 10 and were resistant to microbial degradation. The fluidization and stabilization behavior of the beads was examined in a bench-scale MSFB. The minimum fluidization velocity (Umf) of the beads (0.035 mm s-1) allowed the MSFB to be operated at superficial velocities close to those used in HPLC systems. Against expectations, at high superficial velocities, the stabilized bed of the MSFB had a greater expansion than the unstabilized bed. The PAM beads could be derivatized and activated for soybean trypsin inhibitor immobilization by a standard carbodiimide method, and the affinity separation of trypsin from chymotrypsin was demonstrated. The PAM beads show excellent potential for use in MSFB chromatography. © 1997 John Wiley & Sons, Inc.
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  • 103
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    Isoelectrically trapped enzymatic bioreactors in a multimembrane cell coupled to an electric field: Theoretical modeling and experimental validation with urease (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 110-119 
    Details
    ISSN: 0006-3592
    Keywords: isoelectric membranes ; immobilized reactors ; urease ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A novel type of immobilized enzyme reactor operating under an electric field is here reported: a multicompartment immobilized enzyme reactor (MIER). In this experimental set-up, the enzyme and zwitterionic buffering ions are trapped in between two isoelectric membranes, having isoelectric point (pl) values so far apart as to trap the enzyme by an isoelectric mechanism, while allowing operation at pH optima, even when the latter pH value is quite removed from the enzyme pl. As an example, urease (pl 4.9) is trapped between a pl 4.0 and a pl 8.0 membranes, thus permitting operation (via suitable amphoteric ions buffering at pH 7.5) at the pH of optimum of activity (pH 7.5). The charged product (ammonium ions) quickly leaves the enzyme chamber under the influence of the electric field, thus allowing sustained activity for much longer time periods than in conventional reactors. As an example, while in a batch reactor 90% of original enzyme activity is lost in 200 min, only 2% activity is lost in the same period in the MIER reactor. As an additional bonus, the MIER reactor allows conversion rates of ∼95% in a wide range of substrate concentrations, whereas batch-type reactors rarely achieve better than 50% conversion under comparable experimental conditions. © 1997 John Wiley & Sons, Inc.
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  • 104
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    Metabolic engineering and control analysis for production of aromatics: Role of transaldolase (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 132-138 
    Details
    ISSN: 0006-3592
    Keywords: metabolic engineering ; metabolic control analysis ; transaldolase ; aromatics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Aromatic metabolites in Escherichia coli and other microorganisms are derived from two common precursors: phosphoenolpyruvate (PEP) and erythrose 4-phosphate (E4P). During growth on glucose, the levels of both E4P and PEP are insufficient for high throughput of aromatics because of the low carbon flux through the pentose pathway and the use of PEP in the phosphotransferase system. It has been shown that transketolase and PEP synthase are effective in relieving this limitation and promoting high throughput of aromatics. To determine whether transaldolase, another E4P-producing enzyme, is also a limiting factor in directing carbon flux to the aromatic pathway, E. coli transaldolase gene (tal) was cloned and overexpressed in an aroB strain which excretes 3-deoxy-D-arabinoheptulosonate-7-phosphate (DAHP), the first intermediate in the aromatic pathway. We found that overexpression of transaldolase did significantly increase the production of DAHP from glucose. This result further supports the contention that the supply of E4P is limiting when glucose is the carbon source. However, overexpression of transaldolase in strains which already overexpress transketolase did not show a further increase in production of aromatics. This result was attributed to the saturation of E4P supply when TktA was overexpressed. The flux control of DAHP production was discussed on the basis of Metabolic Control Analysis. © 1997 John Wiley & Sons, Inc.
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  • 105
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    Measurement of local diffusion coefficients in biofilms by microinjection and confocal microscopy (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 151-158 
    Details
    ISSN: 0006-3592
    Keywords: biofilms ; biofilm structure ; diffusivity ; mass transport in biofilms ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new technique for the determination of local diffusion coefficients in biofilms is described. It is based on the microinjection of fluorescent dyes and quantitative analysis of the subsequent plume formation using confocal laser microscopy. The diffusion coefficients of fluorescein (MW 332), TRITC-IgG (MW 150000) and phycoerythrin (MW 240000) were measured in the cell clusters and interstitial voids of a heterogeneous biofilm. The diffusivities measured in the voids were close to the theoretical values in water. Fluorescein had the same diffusivity in cell clusters, voids, and sterile medium. TRITC-IgG did not diffuse in cell clusters, presumably due to binding to the cell cluster matrix. After treatment of the biofilm with bovine serum albumin, binding capacity decreased and the diffusion coefficient could be measured. The diffusivity of phycoerythrin in cell clusters was impeded by 41%, compared to interstitial voids. From the diffusion data of phycoerythrin it was further calculated that the cell cluster matrix had the characteristics of a gel with 0.6 nm thick fibers and pore diameters of 80 nm. © 1997 John Wiley & Sons, Inc.
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  • 106
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    Evidence of bacterial adaptation to monochloramine in Pseudomonas aeruginosa biofilms and evaluation of biocide action model (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 201-209 
    Details
    ISSN: 0006-3592
    Keywords: adaptation ; biofilm ; biocide ; disinfection ; model ; monochloramine ; Pseudomonas ; stress response ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A mathematical model of biocide action against microbial biofilm was tested experimentally by measuring the response of Pseudomonas aeruginosa biofilm to various doses of monochloramine. Pure culture biofilm was developed in continuous flow annular reactors for 7 days, then treated with a 2-, 4-, or 8-h dose of 2 or 4 mg L-1 monochloramine. Some experiments investigated repeated treatment. Disinfection and regrowth of the biofilm were observed by sampling the biofilm for viable and total cell areal densities for up to 100 h following the biocide treatment. A phenomenological mathematical model was fitted to experimental data sets and captured overall trends, but it could not simulate certain experimentally observed features. The model did simulate rapid disinfection followed by steady regrowth. It correctly predicted a much greater decrease in viable than in total cell densities and also correctly captured the shapes of these trajectories. Discrepancies between the model and data included the following: the model predicted faster regrowth than was experimentally observed, the model predicted that a second dose would be more effective than the first dose but the opposite was observed in the experiments, and parameters estimated by fitting one dose concentration could not be used to predict the results of a different dose concentration or a second dose. Discrepancies between model and the experiment were hypothesized to be due to an adaptive stress response by the bacteria, a process not included in the model. A practical implication of this work is that it is more effective to deliver monochloramine in a short concentrated dose as opposed to a longer dose of lower concentration. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 201-209, 1997.
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  • 107
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    Continuous operation of lipase-catalyzed reactions in nonaqueous solvents: Influence of the production of hydrophilic compounds (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 232-237 
    Details
    ISSN: 0006-3592
    Keywords: lipozyme ; esterification ; continuous reactor ; water activity ; organic solvent ; supercritical carbon dioxide ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In the field of biocatalysis in nonaqueous media, water has been identified as a crucial parameter which has to be carefully controlled. This article studies the continuous operation of a water-producing enzymatic reaction, here the esterification of oleic acid by ethanol in n-hexane catalyzed by LipozymeTM. The conversion decreased significantly over time, eventually coming to a lower steady-state level. This would be due to the accumulation of the produced water into the enzyme fixed-bed reactor, n-hexane being unable to evacuate this water out of the reaction vessel, because of the low polarity of this solvent. Therefore the conversion decreased until the produced water could be eliminated by the solvent achieving a steady state with a lower conversion. In supercritical carbon dioxide, a more hydrophilic solvent, steady state is at once obtained. This approach has been extended to reaction producing a hydrophilic compound, here glycerol during the transesterification between triolein and ethanol, and similar conclusions can be made. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 232-237, 1997.
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  • 108
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    Predicting the partition coefficients of a recombinant cutinase in polyethylene glycol/phosphate aqueous two-phase systems (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 248-257 
    Details
    ISSN: 0006-3592
    Keywords: cutinase ; aqueous two-phase systems ; partition ; modeling ; electrostatics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A model for the prediction of protein partition coefficients in aqueous two-phase systems has been developed. This model accounts for both charge-independent and electrostatic effects. The determination of nonelectrostatic effects was based on the model of Eiteman and Gainer for uncharged solutes while the electrostatic contribution was computed using TITRA, a program that uses a continuum electrostatic model to treat charge interactions in proteins and considers the effect of pH and ionic strength. The partition coefficients of Fusarium solani pisi recombinant cutinase have been satisfactorily predicted in polyethylene glycol (PEG) 1000 and phosphate aqueous two-phase systems at a pH range of 6.0-9.0. The model failed to predict the enzyme partitioning behavior at pH 4.5. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 248-257, 1997.
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  • 109
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    Biological breakdown of RDX in slurry reactors proceeds with multiple kinetically distinguishable paths (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 258-267 
    Details
    ISSN: 0006-3592
    Keywords: RDX biotransformation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Biotransformation of RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) in slurry reactors was studied to determine the importance of supplementation of known biodegraders and the type of nutrient source required. Although addition of bacteria to the system increased the biotransformation rates, the increase may not justify the additional work and cost needed to grow the organisms in a laboratory and mix them into the soil. An inexpensive, rich nutrient source, corn steep liquor, was shown to provide sufficient nutrients to allow for the cometabolic biotransformation of RDX. The rate of RDX transformation was not constant throughout the course of the experiment due to the heterogeneous microbial population. Three kinetically distinct phases were observed. Regardless of the process, RDX biotransformation in slurry reactors was reaction rate limited under the test conditions. Model simulations based on experimental results demonstrate that, at cell densities of 5 g/L, bioremediation of RDX-contaminated soil is an attractive clean-up alternative. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 258-267, 1997.
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  • 110
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    Continuous production of a hybrid antibiotic by Streptomyces lividans TK21 pellets in a three-phase fluidized-bed bioreactor (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 601-610 
    Details
    ISSN: 0006-3592
    Keywords: hybrid antibiotic ; continuous fermentation ; pellet ; morphology ; fluidized bed ; Streptomyces ; immobilized cells ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The continuous production of a hybrid antibiotic by a transformed strain of Streptomyces lividans TK21 in a three-phase fluidized bed is studied. Cell aggregates, known as pellets, are used as immobilized cell particles in the bioreactor. A methodology to prepare pellets of a suitable size and morphology is developed. The continuous production of the antibiotic is studied on the basis of decoupling cell growth and antibiotic production, by means of phosphate limitation in the growth medium. The best results are achieved at D = 0.021 h1, with alternate feeding of 0 and 0.05 m M phosphate media. Continuous production of the antibiotic can be maintained at satisfactory levels for periods of 60 days, and stable operation of the bioreactor is achieved during 85 days. Finally, the evolution of the internal structure of the pellets during continuous fermentation is studied. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 601-610, 1997.
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  • 111
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    Factors affecting the fermentative production of a lysozyme-binding antibody fragment in Escherichia coli (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 611-622 
    Details
    ISSN: 0006-3592
    Keywords: single-chain Fv antibody fragment ; recombinant Escherichia coli ; periplasmic space ; fed-batch fermentation ; yeast extract ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Fed-batch fermentation for production of a single-chain Fv antibody fragment (scFv) expressed as a recombinant periplastic protein from Escherichia coli was investigated. A high cell density of 50 g dry cell weight per liter was routinely achieved in a 14-L vessel by controlled exponential feeding of glucose to impose a constant specific growth rate. Following biomass accumulation, induction of the tac promoter by addition of IPTG was accompaied by a linear feed of yeast extract. The concentration of yeast extract feed was found to be highly influential upon both concentration and location of active product. Although scFv fragments were specifically targeted to the periplasmic space, at yeast extract feed rates of 0.72 g/h the final location was largely extracellular (68% to 79%). Total concentrations (extracellular + periplasmic) were of the order of 5 to 8 mg/L. A ten-fold increase in yeast extract supply increased total scFv concentration to almost 200 mg/L and 78% of this yield was retained in the periplasm. Control of such leakage of the recombinant product is fundamental to process design of downstream operations for product recovery. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 611-622, 1997.
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  • 112
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    Effect of bench-scale culture conditions on murine IgG heterogeneity (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 54 (1997), S. 17-25 
    Details
    ISSN: 0006-3592
    Keywords: hybridoma cell culture ; fermentation ; MAb heterogeneity ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A stable murine hybridoma cell line, secreting IgG1 antibodies (7H3) against the soluble type I receptor for Tumor Necrosis Factor (sTNF-R1), was cultivated in two different bioreactor systems, a hollow fiber and a stirred tank fermentor, in order to evaluate the effect of culture conditions on antibody structural and functional heterogeneity. Conventional serum-supplemented and serum-free media were chosen for fermentation in stirred tank bioreactor, whereas only serum-supplemented media were used for hollow fiber cultivation. Extent of glycosylation, determined by lectin binding assays, and charge heterogeneity of murine monoclonal antibodies displayed relevant variations according to the fermentation system used. After complete sugars removal by N-glycosidase F treatment, charge heterogeneity were still observed suggesting the occurrence of additional modifications at the protein level. In vitro culture in serum-supplemented media carried out with the hollow fibre system led to higher productivity but greater antibody charge heterogeneity and differences in lectin-binding profile than cultivation in the stirred tank bioreactor.Results cumulatively indicated that hybridoma cultivation methods, but also cultivation time, influence antibody heterogeneity, both in the protein and sugar moieties. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 17-25, 1997.
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  • 113
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    Improved operational stability of cell-free glucose-fructose oxidoreductase from Zymomonas mobilis for the efficient synthesis of sorbitol and gluconic acid in a continuous ultrafiltration membrane reactor (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 623-629 
    Details
    ISSN: 0006-3592
    Keywords: glucose-fructose oxidoreductase ; Zymomonas mobilis ; free enzyme ; continuous production ; stability ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: For the continuous, enzymatic synthesis of sorbitol and gluconic acid by cell-free glucose-fructose oxidoreductase (GFOR) from Zymomonas mobilis, the principal determinants of productivity have been identified. Most important, the rapid inactivation of the soluble enzyme during substrate conversion can be avoided almost completely when weak bases such as tris(hydroxymethyl)aminomethan or imidazol are used for the titration of the produced gluconic acid and when 5-10 mM dithiothreitol are added to prevent thiol oxidations. With regard to a long-term operational stability of the enzyme for continuous syntheses, thermal deactivation becomes significant at reaction temperatures above 30°C. Without any additional purification being required, the crude cell extract of Z. mobilis can be employed in a continuous ultrafiltration membrane reactor over a time period of more than 250 h without significant decrease in substrate conversion or enzyme activity. The use of soluble GFOR thus appears to be an interesting alternative to employing permeabilized cells of Zymomonas for the production of sorbitol and gluconic acid and may be superior with regard to reactor productivities, at comparable operational stabilities. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 623-629, 1997.
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  • 114
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    Prevention of hybridoma cell death by bcl-2 during suboptimal culture conditions (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 54 (1997), S. 1-16 
    Details
    ISSN: 0006-3592
    Keywords: apoptosis ; hypoxia ; hyperoxia ; growth arrest ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: TB/C3 hybridoma cells were transected with either pEF-MClneopA or pEF bcl2-MClneopA vectors to produce a control cell line (TB/C3 pEF) and a cell line that overexpresses the “antiapoptotic” human bcl-2 protein (TB/C3 bcl2). Flow cytometry analysis of intracellular bcl-2 protein levels enabled near on-line monitoring of the stability of bcl-2 expression in the absence of drug selection. It was possible to maintain spontaneous selection of cells with the overexpression of bcl-2 protein during semicontinuous cultures at very low dilution rates, where cells were subjected to the selective conditions of nutrient limitation and high toxic metabolite concentrations. Interestingly, cells that overexpressed bcl-2 were adapted to suspension culture conditions significantly faster than control cells. Dual fluorescence staining with acridine orange and propidium iodide allowed for discrimination between viable, apoptotic, secondary necrotic, and necrotic cells, respectively. Compared with the usual trypan blue method of establishing culture viability, dual staining demonstrated that under stressful conditions a significant proportion of cells that excluded trypan blue were also undergoing cell death through apoptosis. In batch cultures the overexpression of bcl-2 more than doubled the membrane intact (MI) cell productive period (the integral of Ml cell density with respect to culture time) and increased the monoclonal antibody (mAb) production by approximately 40% when compared with the control cell line. The overexpression of bcl-2 protein also significantly extended the cell integrity and viability by the suppression of apoptosis in conditions of hypoxia, hyperoxia, glutamine deprivation, glucose deprivation, and serum limitation. The suppression of apoptosis in anaerobic conditions suggests that bcl-2 exerts its antiapoptotic activity by a mechanism that does not involve an oxidative reactive pathway. In conditions of excess thymidine, which suppressed cell proliferation, Ml cell density and specific mAb productivity were further enhanced by the overexpression of bcl-2, which suggests the possibility of accomplishing a controlled proliferation in immortalized cell lines without invoking cell death. Cell size and intracellular mAb were increased for TB/C3 bcl2 cells compared with TB/C3 pEF control cells when analyzed by flow cytometry. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 1-16, 1997.
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  • 115
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    Design of surfactants suitable for protein extraction by reversed micelles (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 54 (1997), S. 26-32 
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    ISSN: 0006-3592
    Keywords: reversed micelle ; microemulsion ; protein extraction ; surfactant ; bioseparation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: New surfactants have been synthesized for potential use in reversed micellar protein extraction operations. Preferential solubility of the surfactant in an aliphatic solvent such as hexane, heptane, or isooctane and the formation of reversed micelles accompanied with solubilization of significant quantities of water can be achieved by using strongly hydrophobic, twin alkyl chains as the hydrophobic moiety. Different surfactants having identical water-solubilizing capacities can have significantly different behavior in protein extractions, where extraction efficiency appears to be governed by the nature of the interfacial complex that forms between surfactants and proteins. Bulky surfactant chains provide a steric hindrance to the adsorption of the surfactant to the protein surface, thus inhibiting solvation of the protein/surfactant complex, and hence protein extraction. Under these conditions, a precipitate forms either in the bulk aqueous phase or at the interface. Surfactants that can form a close-packed complex with the protein are excellent protein-solubilizing agents. Dioleyl phosphoric acid (DOLPA) appears to be the best surfactant currently available for protein extraction. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 26-32, 1997.
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    Trehalase immobilization on aminopropyl glass for analytical use (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 54 (1997), S. 33-39 
    Details
    ISSN: 0006-3592
    Keywords: trehalase ; trehalose ; immobilization ; aminopropyl glass ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Trehalase is the enzyme which hydrolyzes the disaccharide trehalose into two α-D-glucose molecules. In this article, we present the immobilization of trehalase on aminopropyl glass particles. The enzyme was extracted from Escherichia coli Mph2, a strain harboring the pTRE11 plasmid, which contains the trehalase gene. The partially purified enzyme had a specific activity of 356 U/mg and could be used for quantifying trehalose in the presence of sucrose, maltose, lactose, starch, and glycogen. Partially purified trehalase was immobilized by covalent coupling with retention of its catalytic activity. The support chosen for the majority of the experiments reported was aminopropyl glass, although spherisorb-5NH2 and chitin were also tested. The immobilized enzyme was assayed continuously for 40 h, at pH 6.0 and 30°C, and no release of enzyme molecules was detected during this procedure. The best condition found for storing the enzyme-support complex was at 4°C in the presence of 25 mM sodium maleate, containing 7 mM β-mercaptoethanol, 1 mM ethylenediaminetetraacetic acid (EDTA), and 50% glycerol. The enzyme under these conditions was stable, retaining approximately 100% of its initial activity for at least 28 days. The immobilized enzyme can be employed to detect trehalose molecules in micromolar concentration. The optimum pH value found was 4.5 and the Km app. 4.9 × 10-3 M trehalose at pH 4.6 and 30°C, with Vmax of 5.88 μmol glucose · min.-1, as calculated by a Lineweaver-Burk plot. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 33-39, 1997.
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    Preliminary characterization of bovine beta-lactoglobulin after its conjugation to polyethylene glycol (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 54 (1997), S. 40-49 
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    ISSN: 0006-3592
    Keywords: pegylation ; whey proteins ; retinol-binding ; conformation ; immunogenicity ; plasma-clearance ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The major component of the whey fraction of bovine milk, β-lactoglobulin (βLG), has been transformed by grafting polyethylene glycol chains either on the thiol group (free and after reduction of the S-S bridges) of the cysteine residues, or on the amino group of the lysine residues and/or of the N-terminal amino acid. Acylation of the protein was achieved at a controlled pH of 7.0 using increasing ratios of activated PEG to βLG. Transformation of the dimeric form into the monomer occurred at least for the fully pegylated adduct. The number of polymer chains fixed per mole of protein was determined by dosage of the free amino functions still present after reaction. The incidence of pegylation on the secondary structure of βLG was evaluated using the Fourier Transform Infrared Spectroscopy (FTIR). Denaturation studies with guanidinium hydrochloride (Gu-HCl) by means of spectrofluorimetric measurements, showed an identical behavior of native as well as of pegylated βLG.The antigenicity of the fully pegylated adduct was examined through antigenic competition towards native βLG. The pegylated protein exhibited less than 1/100 of the native βLG inhibition capacity, that could moreover never be complete. This is thus demonstrating the loss of accessibility for at least multiple conformational epitopes through pegylation procedure.Spectrofluorimetric measurements showed that βLG-N-PEG7 was still able to bind retinol while no effect on the intrinsic fluorescence could be detected by adding palmitic acid. Whether this last ligand binds or not to pegylated βLG is discussed. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 40-49, 1997.
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    Activity, stability, and conformation of methoxypoly(ethylene glycol)-subtilisin at different concentrations of water in dioxane (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 54 (1997), S. 50-57 
    Details
    ISSN: 0006-3592
    Keywords: PEG-subtilisin ; transesterification ; subtilisin ; dioxane ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The transesterification activity, autolysis, thermal stability and conformation of subtilisin Carlsberg, made soluble in dioxane by covalent linking to methoxypoly(ethylene glycol) (PEG), were investigated as a function of the concentration of water in the medium. Electrospray mass spectrometry showed that the modified enzyme preparation was a mixture of proteins containing from 2 to 5 covalently linked PEG chains per subtilisin molecule. PEG-subtilisin catalyzed transesterification between vinyl butyrate and 1-hexanol was optimum at 0.55 MH2O, while hydrolysis prevailed above 2 MH2O. There was a decrease in the overall enzyme activity with increasing water concentration because of autolysis and denaturation of the enzyme. Subtilisin powder and celite-immobilized subtilisin were more stable and less susceptible to autolysis than the PEG-modified enzyme. Circular dichroism and intrinsic protein-fluorescence studies showed that the conformation of PEG-subtilisin did not change as a function of water concentrations between 0 and 9 M. The Km,app value of PEG-subtilisin for 1-hexanol was highly influenced by water, which behaved as a competitive inhibitor in the transesterification reaction with an affinity for the enzyme similar to that of the alcohol. The Km,app for the acylating agent was not significantly modified by water. Lyoprotectants such as sorbitol and free PEG did not influence the activity of PEG-subtilisin but notably increased the activity of subtilisin powder and celite-immobilized subtilisin. The addition of 1.7-5.5 M water, however, rendered enzyme preparations containing no additives as active as those containing the lyoprotectants. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 50-57, 1997.
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    A kinetic model for biological oxidation of ferrous iron by Thiobacillus ferrooxidans (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 478-486 
    Details
    ISSN: 0006-3592
    Keywords: Thiobacillus ferrooxidans ; kinetic model ; biological oxidation ; ferrous iron ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The kinetics of bacterial oxidation of ferrous iron in the presence of Thiobacillus ferrooxidans cells were studied using an initial-rate method. Measurements of the redox potential of the solution during the oxidation of ferrous iron were used to assess the initial rate of the reaction. Effects on the rate of reaction were determined for ferrous iron concentration in the range 0.25 to 30 kg m-3, bacterial concentration in the range 3.25 × 107 to 4.47 × 108 cells mL-1, and temperature in the range 20 to 35°C. Using these experimental results and an approach based on Michaelis-Menten kinetics, a model for biological oxidation of ferrous iron was developed. The model, which incorporates terms for the effect of temperature and substrate and cell inhibition, was successfully used to simulate the full range of experimental data obtained. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 478-486, 1997.
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    Optimization by experimental design of polyacrylamide gel composition as support for enzyme immobilization by entrapment (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 497-506 
    Details
    ISSN: 0006-3592
    Keywords: immobilized enzymes ; polyacrylamide gels ; experimental design ; response surface methodology ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: We have developed a methodology based on experimental design, to optimize a polyacrylamide gel as the support for enzyme immobilization, taking advantage of all the properties which this type of gel has. Monomer and crosslinking agent proportions are responsible for both the porous structure and pore size of the gel. A correct selection of those variables and suitable synthesis conditions leads to an increase in the activity retained by the gel. The path of steepest ascent method was used to obtain the relative maximum activity. The maximum retained activity was chosen with a central composite design in terms of the gel composition. The retained activity in the network, loss activity in the wash water, and loss activity due to steric impediment or blockage was modeled in terms of the variables responsible for the gel structure. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 497-506, 1997.
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    Study of stability of recombinant plasmids during the continuous culture of Bacillus stearothermophilus NUB3621 in nonselective medium (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 507-514 
    Details
    ISSN: 0006-3592
    Keywords: Bacillus stearothermophilus ; continuous culture ; plasmid stability ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The optimal culture conditions for Bacillus stearothermophilus NUB3621 (BGSC 9A5) in chemostat were studied. The results obtained showed that the optimal culture conditions in terms of biomass concentration and maximum growth rate were 65°C, pH 6.8 to 7.2. Dissolved oxygen became growth limiting at pO2 levels below 10%. Furthermore, this strain was transformed with three new hybrid vectors (pPAM2, pPCH2, or pPLY2) constructed by cloning in pRP9, a plasmid based on the thermophilic replicon, pBC1, and three heterologous genes: the α-amylase gene from Bacillus licheniformis, the cholesterol oxidase gene from Streptomyces sp., and the lipase gene from Pseudomonas fluorescens. The influence of several fermentative conditions on segregational and structural stability of the recombinant B. stearothermophilus NUB3621 transformants was studied.The parameters of plasmid loss, that is, rate of plasmid loss (R) and specific growth rate difference (δμ), were calculated. B. stearothermophilus NUB3621 carrying pRP9 showed great segregational stability in all the assayed conditions, exceeding more than 300 generations without significant plasmid loss, whereas NUB3621 carrying pPAM2, pPCH2, or pPLY2 exhibited relatively low plasmid stability. The segregational instability of the recombinant constructs increased by increasing the fermentation temperature, decreased by increasing the dilution rate, and was not affected by the level of dissolved oxygen. On the other hand, plasmid maintenance decreased in minimal medium if compared with the results obtained in complex medium. Restriction analyses carried out on cultures of NUB3621 carrying pRP9, pPAM2, pPCH2, or pPLY2, grown for 200 generations on nonselective media, revealed that all the clones tested contained the parental plasmids. These results indicate that the heterologous inserts did not affect the structural stability of the recombinant plasmids. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 507-514, 1997.
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    How do additives affect enzyme activity and stability in nonaqueous media? (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 54 (1997), S. 67-76 
    Details
    ISSN: 0006-3592
    Keywords: α-chymotrypsin ; buffer salts ; Candida antarctica lipase ; differential scanning calorimetry ; potassium chloride ; sorbitol ; water activity ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The catalytic activities of lyophilized powders of α-chymotrypsin and Candida antarctica lipase were found to increase 4- to 8-fold with increasing amounts of either buffer salts or potassium chloride in the enzyme preparation. Increasing amounts of sorbitol in the chymotrypsin preparation produced a modest increase in activity. The additives are basically thought to serve as immobilization matrices, the sorbitol being inferior because of its poor mechanical properties.Besides their role as supports, the buffer species were indispensable for the transesterification activity of chymotrypsin because they prevented perturbations of the pH during the course of the reaction. Hence, increasing amounts of buffer species yielded a 100-fold increase in transesterification activity. Effects of pH changes were not as predominant in the peptide synthesis and the lipase-catalyzed reactions.Immobilization of the protease on celite resulted in a remarkable improvement of transesterification activity as compared to the suspended protease, even in the absence of buffer species. Immobilization of the lipase caused a small improvement of activity. The activity of the immobilized enzymes was further enhanced 3-4 times by including increasing amounts of buffer salts in the preparation.The inclusion of increasing amounts of sodium phosphate or sorbitol to chymotrypsin rendered the catalyst more labile against thermal inactivation. The denaturation temperature decreased with 7°C at the highest content of sodium phosphate, as compared to the temperature obtained for the denaturation of the pure protein. The apparent enthalpy of denaturation increased with increasing contents of the additives. The enhancement of hydration level and flexibility of the macromolecule upon addition of the compounds partly provides the explanation for the observed results. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 67-76, 1997.
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    Dramatically stabilized phosphotriesterase - polymers for nerve agent degradation (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 54 (1997), S. 105-114 
    Details
    ISSN: 0006-3592
    Keywords: enzymes ; phosphotriesterase ; immobilization ; polyurethane foam ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Phosphotriesterase (EC 3.1.8.1) was immobilized within a polyurethane foam matrix during polymer synthesis using a prepolymer synthesis strategy. In addition to retaining greater than 50% of the enzyme specific activity, numerous benefits were incurred upon immobilization. Orders of magnitude increases in storage and thermal stability (net stabilization energy = 12.5 kJ/mol) were observed without the need for enzyme premodification. The immobilized enzyme system was protease resistant and seemed to display no adverse effects from immobilization, such as an alteration of enzyme function. The organic solvent, dimethyl sulfoxide, also exhibited a stabilizing effect on phosphotriesterase enzyme systems over a range of intermediate concentrations. We attribute these effects in part to direct interaction between the aprotic solvent and metal containing residues present at the enzyme's active site. Our data demonstrate that just 2.5 kg of immobilized enzyme may be sufficient to degrade 30,000 tons of nerve agent in just 1 year. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 105-114, 1997.
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    Production of recombinant proteins in transgenic plants: Practical considerations (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 473-484 
    Details
    ISSN: 0006-3592
    Keywords: transgenic plants ; recombinant protein ; gene expression ; downstream processing ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This review is based on our recent experience in producing the first commercial recombinant proteins in transgenic plants. We bring forward the issues that have to be considered in the process of selecting and developing a winning transgenic plant production system. From the production point of view, transcription, posttranscription, translation, and posttranslation are important events that can affect the quality and quantity of the final product. Understanding the rules of gene expression is required to develop sound strategies for optimization of recombinant protein production in plants. The level of recombinant protein accumulation is critical, but other factors such as crop selection, handling and processing of transgenic plant material, and downstream processing are equally important when considering commercial production. In some instances, the cost of downstream processing alone may determine the economic viability of a particular plant system. Some of the potential advantages of a plant production system such as the high levels of accumulation of recombinant proteins, glycosylation, compartmentalization within the cell, and natural storage stability in certain organs are incentives for aggressively pursuing recombinant protein production in plants. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 473-484, 1997.
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    Continuous mixed strain mesophilic lactic starter production in supplemented whey permeate medium using immobilized cell technology (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 502-516 
    Details
    ISSN: 0006-3592
    Keywords: immobilized cells ; lactic starters ; continuous fermentation ; whey permeate ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The aim of this work was to study a new process for the continuous production of mixed-strain lactic acid bacteria starters using immobilized cells. Three strains of Lactococcus (two Lactococcus lactis subsp. lactis: KB and KBP, and one Lactococcus lactis subsp. lactis biovar diacetylactis: MD) were immobilized separately in κ-carrageenan-locust bean gum gel beads. Continuous fermentations were carried out in a 1 L pH-controlled stirred tank reactor with a 30% (v/v) bead inoculum (strain ratio 1:1:1), continuously fed with a whey UF permeate medium, supplemented with 1.5% yeast extract and 0.1M KCl. The effects of three parameters - pH, temperature (T), dilution rate (D), and their interactions on the composition and activity of the culture in the effluent at pseudosteady state were studied according to a rotatable central composite design, during a 53-day fermentation. The process showed a high biological stability and no strain became dominant, or was eliminated from the bioreactor. The statistical analysis showed that the three strains were differently affected by the studied parameters, and that a large range of effluent starter composition can be achieved by varying D, pH, and T. However, the acidifying characteristics were not affected by the culture conditions. A cross-contamination from other strains of the mixed culture was observed in gel beads entrapping a pure culture at the fermentation onset, and led to a biomass redistribution within the beads. However, the strain ratio (KB:KBP:MD) observed after the 53-day experiment (1:2:2) was close to the initial bead ratio (1:1:1). The beads demonstrated a high mechanical stability throughout the 53-day continuous fermentation. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 502-516, 1997.
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    Relevance of rheological properties of gel beads for their mechanical stability in bioreactors (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 517-529 
    Details
    ISSN: 0006-3592
    Keywords: immobilized cells ; abrasion ; mechanical stability ; fatigue ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The mechanical stability of biocatalyst particles in bioreactors is of crucial importance for applications of immobilized-cell technology in bioconversions. The common methods for evaluation of the strength of polymer beads (mostly force-to-fracture or tensile tests) are, however, not yet proven to be relevant for the assessment of their mechanical stability in bioreactors. Therefore, we tested fracture properties of gel materials and investigated their relevance for abrasion in bioreactors. Abrasion of gel beads was assumed to be a continuous fracturing of the bead surface. At first, three rheological properties were considered: stress at fracture; strain at fracture; and the total fracture energy. If stress at fracture is the most important property, beads having a similar fracture energy, but a smaller stress at fracture, would abrade faster in a bioreactor than beads with a larger stress at fracture; if fracture energy the determining factor, beads that require less energy to fracture would abrade faster than those having a larger fracture energy for the same fracture stress. To determine this, beads of κ-carrageenan and agar (at two different polymer concentrations) were tested for abrasion in four identical bubble columns under the same operating conditions. Agar beads were expected to abrade faster than those of carrageenan because agar had either a lower stress at fracture or a lower fracture energy. However, no correlation between fracture properties and abrasion rate was found in any of the combinations tested. Carrageenan beads abraded faster than those of agar in all combinations. Furthermore, both the stress and strain at fracture of agar and carrageenan beads decreased during the run and those of carrageenan decreased faster, suggesting that the gels are liable to fatigue in different ways. This hypothesis was confirmed by oscillating experiments in which gel samples were subjected to repeated compressions below their fracture levels. Their resistance to compression clearly decreased with the number of oscillations. Fatigue is probably related to the development of microcracks and microfracture propagation within the material. We concluded that: (a) the use of tests based on bead rupture do not provide relevant information on the mechanical stability of gel beads to abrasion; and (b) abrasion of polymer beads is likely to be related to fatigue of the gel materials. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 517-529, 1997.
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    Monitoring of enzymatic hydrolysis of starch by microdialysis sampling coupled on-line to anion exchange chromatography and integrated pulsed electrochemical detection using post-column switching (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 546-554 
    Details
    ISSN: 0006-3592
    Keywords: post-column switching ; microdialysis ; monitoring ; hydrolysates ; integrated pulsed electrochemical detection ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A quantitative evaluation of the hydrolysis of wheat starch using Termamyl, a thermostable α-amylase (endo-1,4-α-d-glucan, glucanohydrolase; EC 3.2.1.78), is reported. Data from the monitoring of the hydrolysis of wheat starch indicated that, after 1 h, glucose and maltooligosaccharides up to DP 7 were the main hydrolysis products and thus enabled optimization of a liquefication step during the production of L-lactic acid. The monitoring system used, both in the on- and off-line mode, was based on continuous flow microdialysis sampling (CFMS) coupled to anion exchange chromatography and integrated pulsed electrochemical detection (IPED). A microdialysis probe equipped with a 5-mm polysulfone (SPS 4005) membrane, with a molecular-weight cut-off of 5 kDa, was used to sample the hydrolysis products of native wheat starch at 90°C. Characteristic fingerprint separations were achieved by anion exchange chromatography after enzymatic hydrolysis. Post-column switching improved the detection and, consequently, also quantification of the hydrolysates as fouling of the electrode could be reduced. Maltooligosaccharide standards were used for quantification and to verify the elution of the hydrolysates by spiking the off-line samples. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 546-554, 1997.
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    Experimental design for the identification of macrokinetic models and model discrimination (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 564-576 
    Details
    ISSN: 0006-3592
    Keywords: D-optimal design ; parameter estimation ; macrokinetics ; model discrimination ; steady state experiments ; nutristatic process control ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An experimental design method for the identification of macrokinetic models was developed applying an extended D-optimal design criterion. The D-optimal design criterion was modified to consider variable measurement variances as well as multivariate macrokinetic models. The macrokinetics of formate dehydrogenase (FDH) production with Candida boidinii were thus identified within 10 steady state experiments in a labscale continuous stirred tank reactor (10 model parameters). Closed loop control (nutristat) was applied to set-up the operating states suggested by this experimental design method. After each set of steady state experiments the quality of macrokinetic parameters was characterized statistically. For model discrimination a parameter discrimination algorithm based on entropy formulations was adapted. Again a multivariate criterion considering variable measurement variances was developed. This discrimination algorithm was applied to discriminate the macrokinetic model of FDH production with Candida boidinii out of 10 different macrokinetic approaches. An unequivocal discrimination result could be obtained calculating model specific probabilities. These were compared with commonly used sum of squares values. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 564-576, 1997.
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    Simulation of penicillin production in fed-batch cultivations using a morphologically structured model (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 593-604 
    Details
    ISSN: 0006-3592
    Keywords: structured model ; fed-batch cultivation ; repeated fed-batch cultivations ; penicillin production ; Penicillium chrysogenum ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A mathematical model is formulated to describe trends in biomass and penicillin formation as well as substrate consumption for fed-batch cultivations. The biomass is structured into three morphological compartments, and glucose and corn steep liquor are considered as substrates for growth. Penicillin formation is assumed to take place in the subapical compartment and in the growing region of the hyphal compartment. Furthermore, it is inhibited by glucose. Model parameters are estimated using an evolutionary algorithm and fitting the model to a standard fed-batch cultivation. The model is validated on experimental data from three different fed-batch cultivations, including two repeated fed-batch cultivations. The model predictions show good agreement with the measurements of biomass and pencillin concentrations for all fed-batch cultivations. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 593-604, 1997.
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    Immobilization of invertase on sepharose-linked enzyme glycosyl recognizing polyclonal antibodies (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 605-609 
    Details
    ISSN: 0006-3592
    Keywords: affinity immobilization ; glycoenzymes ; thermal stability ; non-inhibitory antienzyme antibodies ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Polyclonal antibodies directed against the yeast invertase glycosyls were raised by immunizing rabbits with neoglycoprotein-I and neoglycoprotein-II. The neoglycoproteins were prepared by separately coupling the N-linked large and small molecular weight yeast invertase oligosaccharides respectively to bovine serum albumin with the help of glutaraldehyde. Antibodies specifically recognizing the invertase oligosaccharides were purified from the sera of rabbits immunized with either neoglycoprotein using an affinity column of sepharose 4B-linked yeast invertase. Specific immunoaffinity supports for the immobilization of invertase were constructed by coupling the affinity-purified antineoglycoprotein-I or antineoglycoprotein-II antibodies to cyanogen bromide activated sepharose-4B. Both the affinity adsorbants were effective in binding and improving the thermal stability of invertase. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 605-609, 1997.
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    Reduction of albumin adsorption onto silicon surfaces by Tween 20 (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 618-625 
    Details
    ISSN: 0006-3592
    Keywords: albumin ; silicon ; hydrophobicity ; adsorption ; Tween 20 ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The ability of Tween 20 to reduce the adsorption of albumin on silicon surfaces of different hydrophobicity was investigated by ellipsometry. As expected, protein adsorption was found to depend on the degree of hydrophobicity of the surfaces and on the concentration of the surfactant. A reduction of 90% in albumin adsorption on hydrophobic methylated surfaces by 0.05% Tween 20 was achieved, whereas a reduction of only 15% on hydrophilic surfaces was observed. Experiments of time-dependent protein adsorption in both pure protein and protein-surfactant mixtures were conducted to ascertain the stability of physically adsorbed Tween 20 films on intermediate silicon surfaces. It was found that the adsorbed Tween 20 film was robust and there was no evidence of exchange of the Tween molecules with albumin for up to 240 min exposure. Adsorption minima were confirmed to correlate with minima in contact angle and critical micelle concentration (CMC). © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 618-625, 1997.
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    An optimal strategy to model microbial growth in a multiple substrate environment (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 635-644 
    Details
    ISSN: 0006-3592
    Keywords: optimal growth ; flux towards growth ; E. coli K12 ; multiple substrate ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A comprehensive model is developed based on an optimal strategy describing varied microbial growth phenomenon involving sequential and simultaneous utilization of substrate. The model mimics the complex regulatory process of a cell which results in diverse growth process with the help of simple multi-variable constrained optimization, which aims at maximizing the specific cell growth. The metabolic processes of a cell are represented by simple flux balance equations. The different growth phenomenon exhibited by a microorganism are attributed to different levels of control present inside the cell. Provision is made in the model for these controls, in the form of constraints in the optimization formulation. The model prediction matches well with the experimental data of simultaneous growth of E. coli K12 on a mixture of glucose and organic acids like lactate, pyruvate, and acetate. Moreover, the model predictions are well in agreement with earlier published experimental data for the growth of E. coli K12 on other organic acids like fumarate, α-ketoglutarate, and succinate. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 635-644, 1997.
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    Substrate reactivity as a function of the extent of reaction in the enzymatic hydrolysis of lignocellulose (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 650-655 
    Details
    ISSN: 0006-3592
    Keywords: substrate reactivity ; lignocellulose ; cellulase ; pretreated wood ; property ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In an effort to better understand the role of the substrate in the rapid fall off in the rate of enzymatic hydrolysis of cellulose with conversion, substrate reactivity was measured as a function of conversion. These measurements were made by interrupting the hydrolysis of pretreated wood at various degrees of conversion; and, after boiling and washing, restarting the hydrolysis in fresh buffer with fresh enzyme. The comparison of the restart rate per enzyme adsorbed with the initial rate per enzyme adsorbed, both extrapolated back to zero conversion, provides a measurement of the substrate reactivity without the complications of product inhibition or cellulase inactivation. The results indicate that the substrate reactivity falls only modestly as conversion increases. However, the restart rate is still higher than the rate of the uninterrupted hydrolysis, particularly at high conversion. Hence we conclude that the loss of substrate reactivity is not the principal cause for the long residence time required for complete conversion. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 650-655, 1997.
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    Synthesis of lovastatin with immobilized Candida rugosa lipase in organic solvents: Effects of reaction conditions on initial rates (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 671-680 
    Details
    ISSN: 0006-3592
    Keywords: immobilized enzymes ; Candida rugosa lipase ; organic solvents ; lovastatin ; dielectric constant ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Lipase from Candida rugosa immobilized on a nylon support has been used to synthesize lovastatin, a drug which lowers serum cholesterol levels, by the regioselective acylation of a diol lactone precursor with 2-methylbutyric acid in mixtures of organic solvents. Analogs of lovastatin having a different side chain were also obtained through this method by reacting the diol substrate with different carboxylic acids. The selection of reaction conditions that maximize the initial reaction rate is investigated. Since the diol substrate has very low solubility in non-polar solvents, reaction solvents consisting of mixtures of hexane with a different, more polar cosolvent are considered. For each of the cosolvent mixtures studied, the reaction rate is maximum for an intermediate percentage of cosolvent in hexane. With total concentrations of the diol lactone in the range 6.25-12.5 mM, maximum initial rates correspond approximately to those cosolvent concentrations that permit a complete solubilization of the substrate. At higher cosolvent concentrations, lower rates are obtained. When considering the same dissolved substrate concentration, the reaction rate was found to increase with increasing values of logPmix and decreasing values of the dielectric constant, when varying the composition of a binary solvent mixture. However, when comparing different cosolvents, no general trend with respect to these properties was observed. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56:671-680, 1997.
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    Relationship between mass transfer coefficient and liquid flow velocity in heterogenous biofilms using microelectrodes and confocal microscopy (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 681-688 
    Details
    ISSN: 0006-3592
    Keywords: biofilm ; confocal scanning laser microscopy ; laminar flow ; liquid flow velocity ; mass transfer coefficient ; microelectrodes ; Reynolds number ; Sherwood number ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The relationship between local mass transfer coefficient and fluid velocity in heterogenous biofilms was investigated by combining microelectrodes and confocal scanning laser microscopy (CSLM). The biofilms were grown for up to 7 days and consisted of cell clusters separated by interstitial channels. Mass transfer coefficient depth profiles were measured at specific locations in the cell clusters and channels at average flow velocities of 2.3 and 4.0 cm/s. Liquid flow velocity profiles were measured in the same locations using a particle tracking technique. The velocity profiles showed that flow in the open channel was laminar. There was no flow at the top surface of the biofilm cell clusters but the mass transfer coefficient was 0.01 cm/s. At the same depth in a biofilm channel, the flow velocity was 0.3 cm/s and the mass transfer coefficient was 0.017 cm/s. The mass transfer coefficient profiles in the channels were not influenced by the surrounding cell clusters. Local flow velocities were correlated with local mass transfer coefficients using a semi-theoretical mass transfer equation. The relationship between the Sherwood number (Sh,) the Reynolds number (Re,) and the Schmidt number (Sc) was found using the experimental data to find the dimensionless empirical constants (n1, n2, and m) in the equation Sh = n1 + n2Rem Sc1/3. The values of the constants ranged from 1.45 to 2.0 for n1, 0.22 to 0.28 for n2, and 0.21 to 0.60 for m. These values were similar to literature values for mass transfer in porous media. The Sherwood number for the entire flow cell was 10 when the bulk flow velocity was 2.3 cm/s and 11 when the bulk flow velocity was 4.0 cm/s. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 681-688, 1997.
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    Shift from growth to nutrient-limited maintenance kinetics during biofilter acclimation (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 330-339 
    Details
    ISSN: 0006-3592
    Keywords: biofilter ; kinetics ; maintenance metabolism ; acclimation ; biomass ; nutrient limitation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: During long-term operation of a biofilter, the mandatory absence of net cell growth forces the cells into maintenance metabolism, which is of relatively low rate compared to substrate consumption during the active growth of the acclimation phase. A model based on this shift in metabolism can explain the postacclimation decrease in activity sometimes reported for biofilters. The cessation of growth can be caused by nutrient depletion in the bed. Postacclimation nutrient addition increases activity primarily by allowing a return to the high substrate consumption rate of active growth, and only secondarily helps raise bed activity because of the ultimately higher amount of biomass in the bed. Simulations incorporating the acclimation period and the role of maintenance metabolism predict about 4 logarithms of growth during acclimation of a hexane biofilter, which was confirmed experimentally. Changes in a biofilter's biomass during the acclimation phase can be estimated from substrate conversion data using two approximate methods. The first follows the cumulative amount of substrate converted and uses the estimated yield of cells from substrate during active growth to estimate the total biomass created. The second method follows a rate constant for conversion of substrate in the bed. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 330-339, 1997.
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    Effect of agitation intensities on fungal morphology of submerged fermentation (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 715-726 
    Details
    ISSN: 0006-3592
    Keywords: fungal morphology ; pellets ; hyphae ; hair of pellets ; agitation intensity ; fermentation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Both parallel fermentations with Aspergillus awamori (CBS 115.52) and a literature study on several fungi have been carried out to determine a relation between fungal morphology and agitation intensity. The studied parameters include hyphal length, pellet size, surface structure or so-called hairy length of pellets, and dry mass per-wet-pellet volume at different specific energy dissipation rates. The literature data from different strains, different fermenters, and different cultivation conditions can be summarized to say that the main mean hyphal length is proportional to the specific energy dissipation rate according to a power function with an exponent of -0.25 ± 0.08. Fermentations with identical inocula showed that pellet size was also a function of the specific energy dissipation rate and proportional to the specific energy dissipation rate to an exponent of -0.16 ± 0.03. Based on the experimental observations, we propose the following mechanism of pellet damage during submerged cultivation in stirred fermenters. Interaction between mechanical forces and pellets results in the hyphal chip-off from the pellet outer zone instead of the breakup of pellets. By this mechanism, the extension of the hyphae or hair from pellets is restricted so that the size of pellets is related to the specific energy dissipation rate. Hyphae chipped off from pellets contribute free filamentous mycelia and reseed their growth. So the fraction of filamentous mycelial mass in the total biomass is related to the specific energy dissipation rate as well.To describe the surface morphology of pellets, the hyphal length in the outer zone of pellets or the so-called hairy length was measured in this study. A theoretical relation of the hairy length with the specific energy dissipation rate was derived. This relation matched the measured data well. It was found that the porosity of pellets showed an inverse relationship with the specific energy dissipation rate and that the dry biomass per-wet-pellet volume increased with the specific energy dissipation rates. This means that the tensile strength of pellets increased with the increase of specific energy dissipation rate. The assumption of a constant tensile strength, which is often used in literature, is then not valid for the derivation of the relation between pellet size and specific energy dissipation rate. The fraction of free filamentous mycelia in the total biomass appeared to be a function of the specific energy dissipation in stirred bioreactors. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 715-726, 1997.
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    An indirect optimization method for biochemical systems: Description of method and application to the maximization of the rate of ethanol, glycerol, and carbohydrate production in Saccharomyces cerevisiae (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 758-772 
    Details
    ISSN: 0006-3592
    Keywords: Optimization ; metabolic systems ; linear programming ; S-system representation ; ethanol ; glycerol ; carbohydrates ; Saccharomyces cerevisiae ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Three metabolic models for the production of ethanol, glycerol, and carbohydrates in yeast are optimized with respect to different production rates. While originally nonlinear, all three optimization problems are reduced in such a way that methods of linear programming can be used. The optimizations lead to profiles of enzyme activities that are compatible with the physiology of the cells, which guarantees their viability and fitness, and yield higher rates of the desired final end products than the original systems. In order to increase ethanol rate production at least three times, six enzymes must be modulated. By contrast, when the production of glycerol or carbohydrates is optimized, modulation of just one enzyme (in the case of glycerol) or two enzymes (in the case of carbohydrates) is necessary to yield significant increases in product flux rate. Comparisons of our results with those obtained from other methods show great similarities and demonstrate that both are valid methods. The choice of one or the other method depends on the question of interest. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 758-772, 1997.
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    Fed-batch culture of recombinant NS0 myeloma cells with high monoclonal antibody production (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 783-792 
    Details
    ISSN: 0006-3592
    Keywords: NS0 myeloma cells ; glutamine synthetase ; fed-batch culture ; cellular metabolism ; lactate consumption ; humanized monoclonal antibody ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An amplified NS0 cell line transfected with a vector expressing a humanized monoclonal antibody (MAb) against CD-18 and glutamine synthetase (GS) was cultivated in a 1.5 L fed-batch culture using a serum-free, glutamine-free medium. Concentrated solutions of key nutrient components were fed periodically using a simple feeding control strategy. Feeding amounts were adjusted daily based on the integral of viable cell concentration over time (IVC) and assumed constant specific nutrient consumption rates or yields to maintain concentrations of the key nutrient components around their initial levels. On-line oxygen uptake rate (OUR) measurement was used to aid empirically the adjustment of the feeding time points and amounts by inferring time points of nutrient depletion. Through effective nutritional control, both cell growth phase and culture lifetime were prolonged significantly, resulting in a maximal viable cell concentration of 6.6 × 109 cells/L and a final IVC of 1.6 × 1012 cells-h/L at 672 h. The final MAb concentration reached more than 2.7 g/L. In this fed-batch culture, cellular metabolism shifts were repeatedly observed. Accompanying the culture phase transition from the exponential growth to the stationary phase, lactate, which was produced in the exponential growth phase, became consumed. The time point at which this metabolism shift occurred corresponded to that of rapid decrease of OUR, which most likely was caused by nutrient depletion. This transition coincided with the onset of ammonia, glutamate and glutamine accumulation. With removal of the nutrient depletion by increasing the daily nutrient feeding amount, OUR recovered and viable cell concentration increased, while cell metabolism shifted again. Instead of consumption, lactate became produced again. These results suggest close relationships among nutrient depletion, cell metabolism transition, and cell death. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 783-792, 1997.
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    Application of self-cycling fermentation technique to the production of poly-β-hydroxybutyrate (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 815-820 
    Details
    ISSN: 0006-3592
    Keywords: self-cycling fermentation ; poly-β-hydroxybutyrate ; nutrient deprivation ; Alcaligenes eutrophus ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The production of poly-β-hydroxybutyrate (PHB) by Alcaligenes eutrophus DSM 545 in a cyclone bioreactor was compared using various culture methods: batch, fed-batch, and self-cycling fermentation (SCF) with and without extended periods of nutrient deprivation. SCF is a semi-continuous method that results in a nutrient limitation for every successive generation of cells and, therefore, may have advantages for products whose formation follow secondary metabolite kinetics. Use of the SCF technique without extended nutrient deprivation produced a PHB concentration of 1.2 g L-1 as 40% of the biomass dry weight. With nitrogen deprivation for 4 or 6 h, the concentration of PHB decreased when compared to the standard SCF technique. However, nitrogen deprivation periods of 8 h resulted in an increase in PHB concentration to 2.7 g L-1 or 59% of the biomass dry weight. The nutrient cycling may act to repress PHB accumulation during periods of nitrogen deprivation, unless a time threshold has been reached, after which PHB accumulation occurs as in normal batch culture. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 815-820, 1997.
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    Mass production of thermostable D-hydantoinase by batch culture of recombinant Escherichia coli with a constitutive expression system (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 449-455 
    Details
    ISSN: 0006-3592
    Keywords: thermostable D-hydantoinase ; recombinant E. coli ; constitutive expression ; glycerol ; batch cultivation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: D-Hydantoinase is an industrial enzyme widely used for the synthesis of optically active D-amino acids. A gene encoding thermostable D-hydantoinase of Bacillus stearothermophilus SD-1 has previously been cloned and constitutively expressed by its native promoter in Escherichia coli XL1-Blue (Lee et al., 1996b). In this work, we attempted mass production of the D-hydantoinase by batch culture of the recombinant E. coli using glycerol as a carbon source. The plasmid content in cells increased in proportion to the culture temperature, which resulted in a two- or three-fold increase of the specific D-hydantoinase activity at 37°C compared with that at 30°C. The plasmid was stably maintained over 80 generations. When glycerol was initially added to a concentration of 100 g/L, the final biomass concentration reached about 50 g-dry cell weight/L in a 50 L-scale fermentation, resulting in the specific enzyme production of 3.8 × 104 unit/g-dry cell weight in a soluble form. Glycerol-using batch cultivation of recombinant E. coli was found to be a cost-effective process for the mass production of industrially useful D-hydantoinase. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 449-455, 1997.
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    Application of fluid mechanic and kinetic models to characterize mammalian cell detachment in a radial-flow chamber (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 616-629 
    Details
    ISSN: 0006-3592
    Keywords: cell adhesion ; radial-flow chamber ; hydrodynamic shear ; detachment kinetics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The strength of adhesion and dynamics of detachment of murine 3T3 fibroblasts from self-assembled monolayers were measured in a radial-flow chamber (RFC) by applying models for fluid mechanics, adhesion strength probability distributions, and detachment kinetics. Four models for predicting fluid mechanics in a RFC were compared to evaluate the accuracy of each model and the significance of inlet effects. Analysis of these models indicated an outer region at large radial positions consistent with creeping flow, an intermediate region influenced by inertial dampening, and an inner region dominated by entrance effects from the axially-oriented inlet. In accompanying experiments patterns of the fraction of cells resisting detachment were constructed for individual surfaces as a function of the applied shear stress and evaluated by comparison with integrals of both a normal and a log-normal distribution function. The two functions were equally appropriate, yielding similar estimates of the mean strength of adhesion. Further, varying the Reynolds number in the inlet, Red, between 630 and 1480 (corresponding to volumetric flow rates between 0.9 and 2.1 mL/s) did not affect the mean strength of adhesion. For these same experiments, analysis of the dynamics of detachment revealed three temporal phases: 1) rapid detachment of cells at the onset of flow, consistent with a first-order homogeneous kinetic model; 2) time-dependent rate of detachment during the first 30 sec. of exposure to hydrodynamic shear, consistent with the first-order heterogeneous kinetic model proposed by Dickinson and Cooper (1995); and 3) negligible detachment, indicative of pseudo-steady state after 60 sec. of flow. Our results provide rigorous guidelines for the measurement of adhesive interactions between mammalian cells and prospective biomaterial surfaces using a RFC. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 616-629, 1997.
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    Kinetics and equilibria of condensation reactions between monosaccharide pairs catalyzed by Aspergillus niger glucoamylase (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 9-22 
    Details
    ISSN: 0006-3592
    Keywords: condensation reactions ; disaccharides ; equilibria ; glucoamylase ; kinetics ; monosaccharides ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Arabinose, fructose, galactose, myo-inositol, lyxose, mannose, ribose, and xylose were incubated individually and with glucose in the presence of Aspergillus niger glucoamylase at pH 4.5 and 45°C. Glucoamylase condenses galactose, glucose, and mannose individually into disaccharides. It also produces mixed disaccharides when each of the eight carbohydrates is incubated with glucose. Many products were identified by gas chromatography of the derivatized reaction mixtures followed by mass spectroscopy of the individual chromatographic peaks. Galacto-, gluco-, or mannopyranosyl rings appear to be present at the nonreducing ends of all the disaccharides produced. Molecules linked through primary hydroxyl groups have the highest equilibrium constants of all products formed, since these bonds are thermodynamically favored. However, glucoamylase is capable of forming bonds with many available hydroxyl groups, as previously demonstrated when it was incubated with glucose alone. Formation rates of different bonds linking different residues vary widely. These results demonstrate that glucoamylase has a wide selectivity toward residues it will condense into disaccharides and toward bonds it will form between them. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 9-22, 1997.
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    Comparative studies of Escherichia coli strains using different glucose uptake systems: Metabolism and energetics (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 583-590 
    Details
    ISSN: 0006-3592
    Keywords: 31P NMR ; PTS mutant ; Escherichia coli ; metabolism ; energetics ; glucose uptake system ; galactose symport system ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Modifying substrate uptake systems is a potentially powerful tool in metabolic engineering. This research investigates energetic and metabolic changes brought about by the genetic modification of the glucose uptake and phosphorylation system of Escherichia coli. The engineered strain PPA316, which lacks the E. coli phosphotransferase system (PTS) and uses instead the galactose-proton symport system for glucose uptake, exhibited significantly altered metabolic patterns relative to the parent strain PPA305 which retains PTS activity. Replacement of a PTS uptake system by the galactose-proton symport system is expected to lower the carbon flux to pyruvate in both aerobic and anaerobic cultivations. The extra energy cost in substrate uptake for the non-PTS strain PPA 316 had a greater effect on anaerobic specific growth rate, which was reduced by a factor of five relative to PPA 305, while PPA 316 reached a specific growth rate of 60% of that of the PTS strain under aerobic conditions. The maximal cell densities obtained with PPA 316 were approximately 8% higher than those of the PTS strain under aerobic conditions and 14% lower under anaerobic conditions. In vivo NMR results showed that the non-PTS strain possesses a dramatically different intracellular environment, as evidenced by lower levels of total sugar phosphate, NAD(H), nucleoside triphosphates and phosphoenolpyruvate, and higher levels of nucleoside diphosphates. The sugar phosphate compositions, as measured by extract NMR, were considerably different between these two strains. Data suggest that limitations in the rates of steps catalyzed by glucokinase, glyceraldehyde-3-phosphate dehydrogenase, phosphofructokinase, and pyruvate kinase may be responsible for the low overall rate of glucose metabolism in PPA316. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 583-590, 1997.
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    Macroporous chitin affinity membranes for lysozyme separation (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 610-617 
    Details
    ISSN: 0006-3592
    Keywords: chitin ; chitosan ; macroporous membranes ; affinity separation ; ovalbumin ; lysozyme ; egg white ; affinity membranes ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Macroporous chitin membranes with high, controlled porosity and good mechanical properties have been prepared using a technique developed in this laboratory based on silica particles as porogen. They were employed for the affinity separation of lysozyme. Chitin membranes (1 mm thickness) can be operated at high fluxes (≥1.1 mL/min/cm2) corresponding to pressure drops ≥2 psi. Their adsorption capacity for lysozyme (∼50 mg/mL membrane) is by an order of magnitude higher than that of the chitin beads employed in column separation. In a binary mixture of lysozyme and ovalbumin, the membranes showed very high selectivity towards lysozyme. The effect of some important operation parameters, such as the flow rates during loading and elution were investigated. Lysozyme of very high purity (〉98%) was obtained from a mixture of lysozyme and ovalbumin, and from egg white. The results indicate that the macroporous chitin membranes can be used for the separation, purification, and recovery of lysozyme at large scale. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 610-617, 1997.
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    Dissolved hydrogen concentration as an on-line control parameter for the automated operation and optimization of anaerobic digesters (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 626-634 
    Details
    ISSN: 0006-3592
    Keywords: anaerobic digestion ; on-line control ; hydrogen concentration ; digester overloading ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The use of dissolved hydrogen as an early warning signal of digester failure and a control parameter to operate anaerobic digesters was investigated. A sensitive, on-line method was developed for measuring trace levels of dissolved hydrogen in a semi-permeable membrane, situated within the biomass of a 1 L laboratory anaerobic digester, using trace reduction gas analysis. At normal operating conditions, the dissolved hydrogen partial pressure (2 to 8 Pa) was found to be linearly correlated with the loading rate of the digester, and was a sensitive indicator of the effect of shockloads as well as gradual overloading. An increase in hydrogen partial pressure above a critical concentration of 6.5-7 Pa indicated the initial stage of digester overloading (i.e., volatile fatty acids accumulation). A H2-based computer control system, using a critical hydrogen partial pressure of 6.5 Pa as the setpoint, was found to be effective for the safe operation of a laboratory digester close to its maximum sustainable loading rate. The existence of a relationship between hydrogen level and organic loading rate was also confirmed on a 600 m3 industrial digester, with digester overloading occurring at hydrogen concentrations above 7 Pa. The results suggest that the dissolved hydrogen concentration is capable of being a sensitive on-line parameter for the automated management of anaerobic digesters near their maximum sustainable loading capacity. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 626-634, 1997.
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    New formulae for folding catalysts make them multi-purpose enzymes (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 645-649 
    Details
    ISSN: 0006-3592
    Keywords: protein disulfide isomerase ; prolyl isomerase ; protein folding catalysts ; multi-purpose enzymes ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Whereas protein disulfide isomerase (PDI) and prolyl isomerase (PPI) are considered as efficient protein folding catalysts, very few large scale processes use them because of economical and technical limitations. PDI and PPI were successfully immobilized on cross-linked agarose beads. PDI inactivation during coupling reaction was overcome by oxidizing active site thiols with dimethylsulfoxide and led to a 64% active enzyme. Alternatively, PPI and PDI biotinylation resulted in 100% and 55-66% active enzymes respectively. The use of these modified catalysts suppresses post-refolding purification and enables the design of biochemical reactors. Several other possible applications are also discussed. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 645-649, 1997.
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    Toluene diffusion and reaction in unsaturated Pseudomonas putida biofilms (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 656-670 
    Details
    ISSN: 0006-3592
    Keywords: unsaturated biofilm ; diffusion ; substrate utilization kinetics ; matric water potential ; toluene ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Biofilms are frequently studied in the context of submerged or aquatic systems. However, much less is known about biofilms in unsaturated systems, despite their importance to such processes as food spoilage, terrestrial nutrient cycling, and biodegradation of environmental pollutants in soils. Using modeling and experimentation, we have described the biodegradation of toluene in unsaturated media by bacterial biofilms as a function of matric water potential, a dominant variable in unsaturated systems. We experimentally determined diffusion and kinetic parameters for Pseudomonas putida biofilms, then predicted biodegradation rates over a range of matric water potentials. For validation, we measured the rate of toluene depletion by intact biofilms and found the results to reasonably follow the model predictions. The diffusion coefficient for toluene through unsaturated P. putida biofilm averaged 1.3 × 107 cm2/s, which is approximately two orders of magnitude lower than toluene diffusivity in water. Our studies show that, at the scale of the microbial biofilm, the diffusion of toluene to biodegrading bacteria can limit the overall rate of biological toluene depletion in unsaturated systems. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 656-670, 1997.
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    Performance characteristics of a reversible immunosensor with a heterobifunctional enzyme conjugate as signal generator (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 221-231 
    Details
    ISSN: 0006-3592
    Keywords: immunosensor ; continuous monitoring ; enzyme stability ; rate-limiting factors ; mathematical model ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Factors that control the performance of a reversible immunosensor with an analyte (progesterone)-enzyme (horseradish peroxidase) conjugate as signal generator have been investigated. The conjugate is used in conjunction with two antibodies, which are specific to progesterone and to horseradish peroxidase, immobilized on two spatially separated polypropylene mesh discs. The conjugate and two antibodies are confined to an internal compartment of a microdialyzer by a semipermeable membrane. The small analyte from an external medium permeates across the membrane into the internal compartment where the analyte concentration determines the relative amounts of the bound conjugate on the two solid surfaces. By measuring two signals from the conjugate bound at two separate sites, we experimentally obtained time-response curves to a concentration pulse of the external analyte. A mathematical (kinetic) model describing the sensor system was developed and used for the determination of rate-limiting factors. In semicontinuous monitoring of the analyte concentrations, operation of the immunosensor with the enzyme conjugate as signal generator required special attention to (a) enzyme stability, (b) analyte permeation (dependence on medium components), and (c) kinetics related to the different accessibility to the same antibody of the small analyte (to be measured) vs. the larger counterpart on the enzyme conjugate (for signal generation). © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 221-231, 1997.
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    Expression of green fluorescent protein in insect larvae and its application for heterologous protein production (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 239-247 
    Details
    ISSN: 0006-3592
    Keywords: green fluorescent protein ; baculovirus ; insect larvae ; interleukin-2 ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Many eukaryotic proteins have been successfully expressed in insect cells infected with a recombinant baculovirus derived from the Autographa californica nuclear polyhedrosis virus (AcNPV). There are, however, disadvantages with this cell-based system when carried out in suspension cultures at high bioreactor volume (e.g., limited oxygen transfer, susceptibility to contamination, high cost). These problems can be avoided by using whole larvae as the “reactors.” There are, however, other problems encountered with larvae, one being their inaccessibility for product sampling. To combat this problem, we have investigated the expression of green fluorescent protein (GFP) as a reporter molecule in Trichoplusia ni insect larvae. A high production level of GFPuv (1.58 mg per larva, 26% of total protein) was obtained, enabling the rapid and non-invasive monitoring of GFP. Bright green light was emitted directly from the large opaque carcasses (∼30mm) after illumination with UV light. Based on the green light intensity and a correlation between intensity and GFP mass, we determined the optimal harvest time (c.a. ∼ 3 days post-infection). In parallel experiments, we expressed human interleukin-2 (IL-2) from another recombinant baculovirus with an almost identical expression profile. Since both GFP and IL-2 were rapidly degraded by protease activity during the fourth day post-infection (another disadvantage with larvae), we found an accurate determination of harvest time was critical. Correspondingly, our results demonstrated that GFP was an effective on-line marker for expression of heterologous protein in insect larvae. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 239-247, 1997.
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    Oxidative renaturation of lysozyme at high concentrations (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 54 (1997), S. 221-230 
    Details
    ISSN: 0006-3592
    Keywords: lysozyme ; protein renaturation ; protein folding kinetics ; folding additives ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Newly synthesized cloned gene proteins expressed in bacteria frequently accumulate in insoluble aggregates or inclusion bodies. Active protein can be recovered by solubilization of inclusion bodies followed by renaturation of the solubilized (unfolded) protein. The recovery of active protein is highly dependent on the renaturation conditions chosen. The renaturation process is generally conducted at low protein concentrations (0.01-0.2 mg/mL) to avoid aggregation. We have investigated the potential of successfully refolding reduced and denatured hen egg white lysozyme at high concentrations (1 and 5 mg/mL). By varying the composition of the renaturation media, optimum conditions which kinetically favor proper folding over inactivation were found. Solubilizing agents such as guanidinium chloride (GdmCl) and folding aids such as L-arginine present in low concentrations during refolding effectively enhanced renaturation yields by suppressing aggregation resulting in reactivation yields as high as 95%. Quantitatively the kinetic competition between lysozyme folding and aggregation can be described using first-order kinetics for the renaturation reaction and third-order kinetics for the overall aggregation pathway. The rate constants for both reactions have been found to be strongly dependent on denaturant and thiol concentration. This strategy supercedes the necessity to reactivate proteins at low concentrations using large renaturation volumes. The marked increase in volumetric productivity makes this a viable option for recovering biologically active protein efficiently and in high yield in vitro from proteins produced as inclusion bodies within microbial cells. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 221-230, 1997.
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    Inducing single-cell suspension of BTI-TN5B1-4 insect cells: II. The effect of sulfated polyanions on baculovirus infection (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 54 (1997), S. 206-220 
    Details
    ISSN: 0006-3592
    Keywords: baculovirus ; BTI-TN5B1-4 ; infection ; attachment ; polyanions ; model ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Sulfated polyanions can be used to rapidly induce and maintain single-cell suspensions of BTI-TN5B1-4 insect cells, a cell line which clumps in suspension. Elimination of cell clumping results in a significant increase in volumetric yield of the baculovirus expression vector system. Sulfated polyanions, however, inhibited baculovirus infection of BTI-TN5B1-4. Data from binding studies and fusion assays suggest that the inhibition of infection was not due to the observed reduction in viral attachment rate but to inhibition of viral membrane fusion in the endosome.The three most effective polyanions for inducing single cells are dextran sulfate, pentosan sulfate, and polyvinyl sulfate. At concentrations required for single-cell formation, dextran sulfate and pentosan sulfate did not affect viral infection at multiplicities of infection greater than one plaque forming unit per cell. In contrast, polyvinyl sulfate blocked viral infection even at a high multiplicity of infection of 20 plaque-forming units per cell. To bypass this inhibition, polyvinyl sulfate can be removed by resuspending the cells in fresh medium before virus addition, and then added back to the cell suspension after a substantial amount of virus has been internalized. Alternatively, polyvinyl sulfate can be neutralized with a polycation before virus addition, and an equivalent amount of polyvinyl sulfate added back after most of the virus has been internalized. We present a simple mathematical model of the attachment and entry of baculovirus in BTI-TN5B1-4, which can be used to design appropriate infection regimens. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 206-220, 1997.
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    A novel dielectrophoresis-based device for the selective retention of viable cells in cell culture media (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 54 (1997), S. 239-250 
    Details
    ISSN: 0006-3592
    Keywords: dielectrophoresis ; perfusion cultures ; mammalian cells ; microfabrication technology ; microelectrodes ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Cost-effective production of biopharmaceuticals on a large scale can be carried out by perfusion cultures of mammalian cells. One problem with this mode of operation for submerged free-cell cultures is the requirement for an efficient cell separation device located in the effluent stream. The present work investigates the potential for the development of a novel dielectrophoresis-based cell separator, capable of providing selective retention of viable cells in cell culture media, which are highly conductive. Predictions of the dielectrophoretic (DEP) response in culture media were first obtained through a series of DEP-levitation experiments. Subsequently, a prototype microelectrode “filter” was microfabricated and tested with C174 myeloma cell suspensions of density 1 × 106 cells/mL. The optimum frequency range for selective retention of viable cells was found in the range 5-15 MHz. A maximum separation efficiency of 98% was achieved at 10 MHz, with an applied peak-to-peak voltage of 30 V (maximum field strength of 105 V/m) and a flow rate of 30 mL/h which corresponds to a superficial velocity of 5.23 cm/h through the DEP-filter channels. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 239-250, 1997
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    Model development for horseradish peroxidase catalyzed removal of aqueous phenol (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 54 (1997), S. 251-261 
    Details
    ISSN: 0006-3592
    Keywords: horseradish peroxidase ; kinetic model ; phenol removal ; parameter estimation ; enzyme inactivation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Once activated by hydrogen peroxide, horseradish peroxidase (HRP) catalyzes the oxidation of aqueous aromatic compounds to produce high molecular weight polymers of low solubility. A pseudo steady-state kinetic model of the HRP-hydrogen peroxide-aromatic compound system was modified to incorporate enzyme inactivation mechanisms in order to improve its predictive ability. The kinetic constants of the model were calibrated using a series of experimental data sets. The model's ability to predict the time-dependent removal of phenol within the range of 0.5-6 mM from a batch reactor was validated. The model accounts for permanent losses of enzyme activity through inactivation by free radicals as well as interaction with end-product polymers as they form. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 251-261, 1997
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    Kinetic studies of Chromobacterium viscosum lipase in AOT water in oil microemulsions and gelatin microemulsion-based organogels (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 54 (1997), S. 416-427 
    Details
    ISSN: 0006-3592
    Keywords: esterification ; hydrophobic organogel ; immobilized enzyme ; 1H-NMR ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Kinetic studies have shown that octyl decanoate synthesis by Chromobacterium viscosum (CV) lipase in sodium bis-2-(ethylhexyl) sulfosuccinate (AOT) water in oil (w/o) microemulsions occurs via the nonsequential (ping-pong) bi bi mechanism. There was evidence of single substrate inhibition by decanoic acid at high concentrations. Initial rate data yielded estimates for acid and alcohol Michaelis constants of ca. 10-1 mol dm-3 and a maximum rate under saturation conditions of ca. 10-3 mol dm-3 s-1 for a lipase concentration of 0.36 mg cm-3. CV lipase immobilized in AOT microemulsion-based organogels (MBGs) was also found to catalyze the synthesis of octyl decanoate according to the ping-pong bi bi mechanism. Reaction rates were similar in the free and immobilized systems under comparable conditions. Initial rates at saturating (but noninhibiting) substrate concentrations were first order with respect to CV lipase concentration in both w/o microemulsions and the MBG/oil systems. Gradients yielded an apparent kcat = 4.4 × 10-4 mol g-1 s-1 in the case of w/o microemulsions, and 6.1 × 10-4 mol g-1 s-1 for CV lipase immobilized in the MBGs. A third system comprising w/o microemulsions containing substrates and gelatin at concentrations comparable to those employed in the MBG formulations, provided a useful link between the conventional liquid microemulsion medium and the solid organogels. The nongelation of these intermediate systems stems from the early inclusion of substrate during a modified preparative protocol. The presence of substrate appears to prevent the development of a percolated microstructure that is thought to be a prerequisite for MBG formation. FT-NMR was employed as a semicontinuous in situ assay procedure. The apparent activity expressed by CV lipase in compositionally equivalent liquid and solid phase gelatin-containing systems was similar. An apparent activation energy of 24 ± 2 kJ mol-1 was determined by 1H-NMR for esterification in gelatin-containing w/o microemulsions. This value agrees with previous determinations for CV lipase-catalyzed synthesis of octyl decanoate in “conventional” w/o microemulsions and MBG/oil systems. The similarities in lipase behavior are consistent with the claim, based largely on structural measurements, that the physico-chemical properties of the lipase-containing w/o microemulsion are to a large extent preserved on transformation to the daughter organogel. The close agreement of apparrent activation energies suggests that substrate mass transfer is not rate determining in the three studied systems. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54:416-427, 1997.
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    Use of flow field-flow fractionation for the rapid quantitation of ribosome and ribosomal subunits in Escherichia coli at different protein production conditions (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 54 (1997), S. 461-467 
    Details
    ISSN: 0006-3592
    Keywords: flow field-flow fractionation ; ribosomes ; sub-units ; quantitation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Asymmetrical flow field-flow fractionation was used for rapid (8-14 min) separation of ribosomes and their subunits. The amount of ribosomes and the mass fraction of ribosomes was determined in growing Escherichia coli cells. These quantities changed significantly at different growth phases. Ribosomal composition was monitored after the insertion of a protein-encoding plasmid and after the addition of an antibiotic agent. The results suggest that the method will be useful in studies of, e.g., the relationships between the protein production capacity of cells and the ribosomal composition. The analysis time is substantially shorter than ultracentrifugation run times. © 1977 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 461-467, 1997.
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    A mathematical model of the trafficking of acid-dependent enveloped viruses: Application to the binding, uptake, and nuclear accumulation of baculovirus (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 54 (1997), S. 468-490 
    Details
    ISSN: 0006-3592
    Keywords: baculovirus ; insect cells ; infection ; internalization ; enveloped viruses ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A quantitative understanding of virus trafficking would be useful in treating viral-mediated diseases, developing protocols for viral gene therapy, designing infection regimens for viral expression systems, and optimizing vaccine and recombinant protein production. Here, we present a mathematical model of the attachment, internalization, endosomal fusion, lysosomal routing, and nuclear accumulation of baculovirus in SF21 insect cells. The model accounts for multivalent bond formation of the virus with cell surface receptors. The model mimics accurately the experimental trafficking dynamics of the virus at both low and high virion to cell ratios, and estimates a receptor number of 11,000 per cell. A significant amount of virus was degraded intracellularly. Independent of the virion to cell ratio, half of the internalized virus was degraded with the rest accumulating in the nucleus. The formalism used in the model may be generally useful for other acid-dependent enveloped viruses. A subset of the model has been used previously to describe the trafficking of Semliki Forest virus, an acid-dependent enveloped RNA virus.Two pathways have previously been implicated for the in vitro entry of the budded form of the baculovirus: adsorptive endocytosis and plasma membrane fusion. Experimental evidence is presented which strongly suggests that the physical number of viruses entering by plasma membrane fusion is not significant relative to receptor-mediated endocytosis. © 1997 John Wiley & Sons, Inc., Biotechnol Bioeng 54: 468-490, 1997.
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    Reductive dechlorination of PCB-contaminated raisin river sediments by anaerobic microbial granules (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 182-190 
    Details
    ISSN: 0006-3592
    Keywords: dechlorination ; bioremediation ; PCBs ; sediments ; anaerobic granules ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A polychlorinated biphenyl (PCB)-dechlorinating anaerobic microbial consortium, developed in a granular form, demonstrated extensive dechlorination of PCBs present in Raisin River sediments at room (20° to 22°C) and at a relatively low (12°C) temperature. Highly chlorinated PCB congeners were dechlorinated and less chlorinated compounds were produced. The homolog comparison showed that tri-, tetra-, penta-, hexa-, and heptachlorobiphenyl compounds decreased significantly, and mono- and dichlorobiphenyl compounds increased. After 32 weeks of incubation at 12°C, the predominant less chlorinated products included 2-, 4-, 2-2/26-, 24-, 2-4-, 24-2-, 26-2-, and 26-4-CB. Among these, 24- and 24-2-CB did not accumulate at room temperature, suggesting a further dechlorination of these congeners. Predominantly meta dechlorination (i.e., pattern M) was catalyzed by the microbial consortium in the granules. Dechlorination in the control studies without granules was not extensive. This study is the first demonstration of enhanced reductive dechlorination of sediment PCBs by an exogenous anaerobic microbial consortium. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 182-190, 1997.
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    Modeling microbial chemotaxis in a diffusion gradient chamber (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 191-205 
    Details
    ISSN: 0006-3592
    Keywords: bacterial chemotaxis ; chemoattractant ; mathematical model ; cell motility ; cell migration ; diffusion gradient chamber ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The diffusion gradient chamber (DGC) has proven to be a useful experimental tool for studying population-level microbial growth and chemotaxis. A mathematical model capable of reproducing the population-level patterns formed as a result of cellular growth and chemotaxis in the DGC has been developed. The model consists of coupled partial differential balance equations for cells, chemoattractants, and a nutrient, which are solved simultaneously by the alternating direction implicit method. Modeling simulation results were compared with population-level migration patterns of Escherichia coli growing on glycerol and responding to a gradient of the chemoattractant aspartate for two different initial conditions. To accurately reproduce the experimental results, a second chemoattractant equation was necessary. The second chemoattractant has been identified as oxygen by directly measuring oxygen gradients in the DGC. Important trends observed experimentally and reproduced by the model include the formation of a chemotactic wave, a reduction in the wave velocity as it encounters higher chemoattractant concentrations, and chemotaxis in response to two different chemoattractants simultaneously. The model was also used to study the relative magnitude of cell fluxes due to random motility and chemotaxis, and the suppression of chemotaxis due to receptor saturation. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 191-205, 1997.
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    Modeling the growth and proteinase A production in continuous cultures of recombinant Saccharomyces cerevisiae (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 447-454 
    Details
    ISSN: 0006-3592
    Keywords: plasmid stability ; protein production ; proteinase A ; Saccharomyces cerevisiae ; modeling ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Overexpression of the homologous protein proteinase A (PrA) in Saccharomyces cerevisiae has been achieved by inserting the PrA gene (PEP4) with its own promoter on a 2μ multicopy plasmid. With this system the specific PrA production rate was found to be described well by a linear function of the oxidative glucose metabolism, the reductive glucose metabolism, and the oxidative ethanol metabolism, with a significant lower yield resulting from the reductive glucose metabolism compared with the oxidative glucose metabolism. To describe the experimental data, a simple mathematical model has been set up. The model is based on an assumption of a limited respiratory capacity as suggested by Sonnleitner and Käppeli but extended to describe production of an extracellular protein. The model predicts correctly the critical dilution rate to be between 0.15 and 0.16 h-1, the decrease in the biomass yield above the critical dilution rate, and the production of proteinase A at different dilution rates. Both the experimental data and model simulations suggest that the optimum operating conditions for protein production is just at the critical dilution rate. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 447-454, 1997.
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    Novel preparation method for surfactant-lipase complexes utilizing water in oil emulsions (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 455-460 
    Details
    ISSN: 0006-3592
    Keywords: enzyme ; biocatalyst ; lipase ; organic solvent ; emulsion ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A novel preparation method for surfactant-lipase complexes has been developed utilizing water in oil emulsions. In order to optimize the preparation conditions, we have investigated the effects of several operational parameters on the enzymatic activity of the surfactant-lipase complexes in organic media. When a nonionic surfactant was employed under optimal preparation conditions [alkaline pH 8-10, organic/aqueous = 90/10 (v/v), concentration of surfactant, 10 mM[, the surfactant-lipase complex efficiently catalyzed the esterification of benzyl alcohol with lauric acid in organic media. The esterification rate of the surfactant-lipase complex was increased over 16-fold relative to the native powder lipase. Furthermore, the lipase complex showed high storage stability. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 455-460, 1997.
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    Unusual salt and solvent dependence of a protease from an extreme halophile (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 471-479 
    Details
    ISSN: 0006-3592
    Keywords: halophilic protease ; stability ; organic cosolvents ; salting out ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An extracellular protease has been purified from the extreme halophile, Halobacterium halobium. The irreversible inactivation kinetics of this halophilic protease in salt concentrations below 4M consists of autolytic and nonautolytic (steady-state denaturation) components. Addition of organic solvents has a dramatic effect on enzyme stability in low salt media. For example, in 0.36M NaCl, the inactivation rate constant for the nonautolytic component in 20% (v/v) ethylene glycol is ca. 3 orders of magnitude lower than in 20% (v/v) tetrahydrofuran. Enzyme stability in different aqueous/organic solvent mixtures correlates strongly to the salting-out capacity of the solvent. Solvents that act to increase the apparent hydrophobicity of the enzyme's core stabilize the enzyme in much the same way as salting-out salts. This mechanism is not important for the nonhalophilic protease, subtilisin Carlsberg, and demonstrates that halophilic enzymes have evolved highly specialized reaction medium requirements. Moreover, through the use of organic solvents, it is shown that high concentrations of salts are not absolutely necessary for high enzyme stability, and this may have important process considerations. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 471-479, 1997.
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    Kinetics of U(VI) reduction by a dissimilatory Fe(III)-reducing bacterium under non-growth conditions (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 490-496 
    Details
    ISSN: 0006-3592
    Keywords: uranium ; kinetics ; precipitation ; shewanella ; metal reduction ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Dissimilatory metal-reducing microorganisms may be useful in processes designed for selective removal of uranium from aqueous streams. These bacteria can use U(VI) as an electron acceptor and thereby reduce soluble U(VI) to insoluble U(IV). While significant research has been devoted to demonstrating and describing the mechanism of dissimilatory metal reduction, the reaction kinetics necessary to apply this for remediation processes have not been adequately defined. In this study, pure culture Shewanella alga strain BrY reduced U(VI) under non-growth conditions in the presence of excess lactate as the electron donor. Initial U(VI) concentrations ranged from 13 to 1680 μM. A maximum specific U(VI) reduction rate of 2.37 μmole-U(VI)/(mg-biomass h) and Monod half-saturation coefficient of 132 μM-U(VI) were calculated from measured U(VI) reduction rates. U(VI) reduction activity was sustained at 60% of this rate for at least 80 h. The initial presence of oxygen at a concentration equal to atmospheric saturation at 22°C delays but does not prevent U(VI) reduction. The rate of U(VI) reduction by BrY is comparable or better than rates reported for other metal reducing species. BrY reduces U(VI) at a rate that is 30% of its Fe(III) reduction rate. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 490-496, 1997.
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    Tc(VII) reduction and accumulation by immobilized cells of Escherichia coli (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 505-510 
    Details
    ISSN: 0006-3592
    Keywords: bioreduction ; bioaccumulation ; immobilized cells ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Resting cells of Escherichia coli, immobilized in a flow-through bioreactor, coupled the oxidation of formate or hydrogen to Tc(VII) reduction and removal from solution. Cells, pregrown anaerobically in a hollow-fiber membrane bioreactor, were challenged with 50 μM Tc(VII) in a carrier solution of phosphate-buffered saline. The radionuclide accumulated within the membrane component of the reactor, corresponding to the localization of the cells. Negligible Tc removal was noted in a reactor containing a mutant deficient in active Tc(VII) reductase, when supplied with formate as an electron donor. Formate or hydrogen was supplied as the electron donor for Tc(VII) reduction to cells immobilized in reactors operated in transverse (crossflow) and direct (dead-end filtration) modes, respectively. Flow-rate activity relationships were used to compare the performance of the reactors. A flow rate of 2.4 mL h-1 supported the removal of 50% of the Tc from solution in a reactor operated in transverse mode with formate as an electron donor. In contrast, a flow rate of 0.7 mL h-1, supported comparable Tc removal when hydrogen was introduced to a reactor operated in direct mode. The reduced reactor efficiency, when hydrogen was used as an electron donor, could be attributed, in part, to poor delivery of the gas to the cells. The biocatalyst was highly stable in the reactor; no loss in activity was noted over 200 h of continuous use. © 1997 John Wiley & Sons Inc. Biotechnol Bioeng 55: 505-510, 1997.
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    Kinetic characterization of mass transfer limited biodegradation of a low water soluble gas in batch experiments - Necessity for multiresponse fitting (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 511-519 
    Details
    ISSN: 0006-3592
    Keywords: ethene ; kinetics ; biodegradation ; mass transfer ; multiresponse fitting ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A method was developed to characterize the kinetics of biodegradation of low water soluble gaseous compounds in batch experiments. The degradation of ethene by resting Mycobacterium E3 cells was used as a model system. The batch degradation data were recorded as the progress curve (i.e., the time course of the ethene concentration in the headspace of the batch vessel). The recorded progress curves, however, suffered gas:liquid mass transfer limitation. A new multiresponse fitting method had to be developed to allow unequivocal identification of both the affinity coefficient, Kaff, and the gas:liquid mass transfer coefficient, Kla, in the batch vessel from the mass transfer limited data. Simulation showed that the Kaff estimate obtained is influenced by the dimensionless (volumetric basis) ethene gas:liquid partitioning coefficient (H). In the fitting procedure, Monod, Teissier, and Blackman biokinetics were evaluated for characterization of the ethene biodegradation process. The fits obtained reflected the superiority of the Blackman biokinetic function. Overall, it appears that resting Mycobacterium E3 cells metabolizing ethene at 24°C have, using Blackman biokinetics, a maximum specific degradation rate, vmax, of 10.2 nmol C2H4 mg-1 CDW min-1, and an affinity coefficient, Kaff.g, expressed in equilibrium gas concentration units, of 61.9 ppm, when H is assumed equal to 8.309. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 511-519, 1997.
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    Kinetic studies on hybridoma cells immobilized in fixed bed reactors (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 535-541 
    Details
    ISSN: 0006-3592
    Keywords: hybridoma ; fixed bed ; metabolism ; kinetic model ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Cultures with immobilized hybridoma cells were performed in fixed bed systems. “Steady state” values for volume-specific substrate uptake and metabolite production rates were determined at various perfusion rates and superficial flow velocities of the medium within the carrier matrix. Data from fixed bed volumes between 50 and 600 ml did not show any difference. The volume-specific glutamine and glucose uptake rate turned out to be independent of the superficial flow velocity, but decreased with decreasing glutamine and glucose concentration. The volume-specific oxygen uptake rate increased with increasing superficial flow velocity and substrate concentration, respectively. A similar behavior was observed for the ratio between oxygen and glucose uptake rate. The production rate for monoclonal antibodies was neither affected by the substrate concentration nor by the superficial flow velocity. The metabolic parameters of the immobilized cells were put into kinetic equations and compared to those of suspended cells. It could be concluded that the metabolism of the immobilized cells is determined by the oxygen supply within the macroporous carriers. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 535-541, 1997.
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    Production of recombinant bacterial endoglucanase as a co-product with ethanol during fermentation using derivatives of Escherichia coli KO11 (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 547-555 
    Details
    ISSN: 0006-3592
    Keywords: ethanol ; cellulose ; hemicellulose ; endoglucanase ; cellulase ; lignocellulose ; biomass ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This study demonstrates a new approach to reduce the amount of fungal cellulase required for the conversion of cellulose into ethanol. Escherichia coli KO11, a biocatalyst developed for the fermentation of hemicellulose syrups, was used to produce recombinant endoglucanase as a co-product with ethanol. Seven different bacterial genes were expressed from plasmids in KO11. All produced cell-associated endoglucanase activity. KO11(pLOI1620) containing Erwinia chrysanthemi celZ (EGZ) produced the highest activity, 3,200 IU endoglucanase/L fermentation broth (assayed at pH 5.2 and 35°C). Recombinant EGZ was solubilized from harvested cells by treatment with dilute sodium dodecyl sulfate (12.5 mg/ml, 10 min, 50°C) and tested in fermentation experiments with commercial fungal cellulase (5 filter paper units/g cellulose) and purified cellulose (100 g/L). Using Klebsiella oxytoca P2 as the biocatalyst, fermentations supplemented with EGZ as a detergent-lysate of KO11(pLOI1620) produced 14%-24% more ethanol than control fermentations supplemented with a detergent-lysate of KO11(pUC18). These results demonstrate that recombinant bacterial endoglucanase can function with fungal cellulase to increase ethanol yield during the simultaneous saccharification and fermentation of cellulose. © 1997 Wiley & Sons, Inc. Biotechnol Bioeng 55: 547-555, 1997.
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    Numerical modeling and uncertainties in rate coefficients for methane utilization and TCE cometabolism by a methane-oxidizing mixed culture (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 320-331 
    Details
    ISSN: 0006-3592
    Keywords: numerical modeling ; uncertainty ; statistics ; cometabolism ; trichloroethylene ; methanotroph ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The rates of methane utilization and trichloroethylene (TCE) cometabolism by a methanotrophic mixed culture were characterized in batch and pseudo-steady-state studies. Procedures for determination of the rate coefficients and their uncertainties by fitting a numerical model to experimental data are described. The model consisted of a system of differential equations for the rates of Monod kinetics, cell growth on methane and inactivation due to TCE transformation product toxicity, gas/liquid mass transfer of methane and TCE, and the rate of passive losses of TCE. The maximum specific rate of methane utilization (kCH4) was determined by fitting the numerical model to batch experimental data, with the initial concentration of active methane-oxidizing cells (X0a) also used as a model fitting parameter. The best estimate of kCH4 was 2.2 g CH4/g cells-d with excess copper available, with a single-parameter 95% confidence interval of 2.0-2.4 mg/mg-d. The joint 95% confidence region for kCH4 and X0a is presented graphically. The half-velocity coefficient (KS,CH4) was 0.07 mg CH4/L with excess copper available and 0.47 mg CH4/L under copper limitation, with 95% confidence intervals of 0.02-0.11 and 0.35-0.59 mg/L, respectively. Unique values of the TCE rate coefficients kTCE and KS,TCE could not be determined because they were found to be highly correlated in the model fitting analysis. However, the ratio kTCE/KS,TCE and the TCE transformation capacity (TC) were well defined, with values of 0.35 L/mg-day and 0.21 g TCE/g active cells, respectively, for cells transforming TCE in the absence of methane or supplemental formate. The single-parameter 95% confidence intervals for kTCE/KS,TCE and TC were 0.27-0.43 L/mg-d and 0.18-0.24 g TCE/g active cells, respectively. The joint 95% confidence regions for kTCE/KS,TCE and TC are presented graphically. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 320-331, 1997.
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    Regulation of growth and adhesion of cultured cells by insulin conjugated with thermoresponsive polymers (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 339-344 
    Details
    ISSN: 0006-3592
    Keywords: cell culture ; tissue engineering ; thermoresponsive polymer ; cell adhesion ; insulin conjugate ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: We developed a new biomaterial for use in cell culture. The biomaterial enabled protein-free cell culture and the recovery of viable cells by lowering the temperature without the aid of supplements. Insulin was immobilized and a thermoresponsive polymer was grafted onto a substrate. We investigated the effect of insulin coupling on the lower critical solution temperature (LCST) of the thermoresponsive polymer, poly(N-isopropylacrylamide-co-acrylic acid), using polymers that were ungrafted, or coupled with insulin. The insulin conjugates were precipitated from an aqueous solution at high temperatures, but they were soluble at low temperatures. The LCST was not significantly affected by the insulin coupling. The thermoresponsive polymer was grafted to glow-discharged polystyrene film and covalently conjugated with insulin. The surface wettability of the conjugate film was high at low temperatures and low at high temperatures. The amounts of immobilized insulin required to stimulate cell growth were 1-10% of the amount of free insulin required to produce the same effect. The maximal mitogenic effect of immobilized insulin was greater than that of free insulin. About half of the viable cells was detached from the film only by lowering the temperature. The recovered cells proliferated normally on new culture dishes. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 339-344, 1997.
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    Selective displacement chromatography of proteins (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 119-129 
    Details
    ISSN: 0006-3592
    Keywords: selective displacement chromatography ; protein purification ; on-line monitoring ; ion-exchange chromatography ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In contrast to high molecular weight polyelectrolyte displacers, the efficacy of low molecular weight displacers are dependent on both mobile phase salt and displacer concentration. This sensitivity to the operating conditions opens up the possibility of carrying out selective displacement where the product(s) of interest can be selectively displaced while the low affinity impurities can be desorbed in the induced salt gradient ahead of the displacement train, and the high affinity impurities either retained or desorbed in the displacer zone. This type of displacement combines the operational advantages of step gradient and the high resolution inherent in a true displacement process, in a single operation. Theoretical expressions are presented for establishing selective displacement operating conditions (initial salt concentration, displacer concentration) based on the Steric Mass Action parameters of the displacer and the linear Steric Mass Action parameters of the feed proteins. Experimental results are presented to elucidate the concept of selective displacement in both cation and anion exchange systems. A mixture of α-lactalbumin and β-lactoglobulin A and B has been used for anion-exchange systems; a four-protein mixture consisting of ribonuclease B, bovine and horse heart cytochrome c, and lysozyme has been employed in cation exchange systems. This article also demonstrates that on-line monitoring can be readily employed for the selective displacement process, thus facilitating the scale-up and control of the process. This work sets the stage for the development of robust large scale high resolution separations using selective displacement chromatography. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 119-129, 1997.
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    Integration of charged membrane into perstraction system for separation of amino acid derivatives (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 162-167 
    Details
    ISSN: 0006-3592
    Keywords: perstraction ; amino acid derivative ; partition coefficient ; charged membrane ; electrostatic rejection ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The integration of a charged membrane into a perstraction system for high selective separation is reported. A mixture of N-(benzyloxycarbonyl)-L-aspartic acid (ZA), L-phenylalanine methyl ester (PM), and N-(benzyloxycarbonyl)-L-aspartyl-L-phenylalanine methyl ester (ZAPM) was used as the model solution. The aqueous phase containing ZA, PM, and ZAPM was adjusted to pH 6 and was contacted with tert-amyl alcohol through a charged membrane. Seven different ion-exchange membranes and two different microfiltration membranes were tested for the separation system. Only ZAPM could permeate into the organic phase through SELEMION AMV and ASV. The separations between ZA and ZAPM and between PM and ZAPM were performed by biphasic extraction and electrostatic rejection, respectively. The permeabilities of ZAPM were higher than those of PM for all experiments using the ion-exchange membranes, although the molecular weight of ZAPM is larger than that of PM. The membrane that had a smaller pore size showed higher ZAPM selectivity. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 162-167, 1997.
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    Response of the central metabolism of Corynebacterium glutamicum to different flux burdens (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 168-180 
    Details
    ISSN: 0006-3592
    Keywords: metabolic fluxes ; metabolite balance ; NMR spectroscopy ; amino acid production ; bidirectional fluxes ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: To evaluate the importance of reactions within the central metabolism under different flux burdens the fluxes within the pentose phosphate pathway (PPP), as well as the other reactions of the central metabolism, were intensively analyzed and quantitated. For this purpose, Corynebacterium glutamicum was grown with [1-13C]glucose to metabolic and isotopic steady state and the fractional enrichments in precursor metabolites (e.g., pentose 5-phosphate) were quantified. Matrix calculus was used to express these data together with metabolite mass data. The detailed analysis of the dependence of 13C enrichments on exchange fluxes enabled the transketolase-catalyzed exchange rate (2 pentose 5-phosphate ↔ sedoheptulose 7-phosphate + glyceraldehyde 3-phosphate) to be quantified as 74.3% (molar metabolite flux) at a net flux of 10.3% and the exchange rate (pentose 5-phosphate + erythrose 4-phosphate ↔ fructose 6-phosphate + glyceraldehyde 3-phosphate) to be quantified as 5.6% at a net flux of 8.1%. The flux entering the tricarboxylic acid cycle was 93.3%. The same comprehensive flux analysis as performed for the nonexcreting condition was done with the identical strain that had been forced to excrete L-glutamate. Because we had already quantified the fluxes for L-lysine excretion with an isogenic strain, three directly comparable flux situations are thus available. Consequently, this comparison permits a direct cause-and-effect relationship to be specified. In response to the different flux burdens of the cell, the PPP flux decreased from a maximum of 67% to 26%, with the glycolytic flux increasing accordingly. The carbon flux through isocitrate dehydrogenase increased from 20% to 36%. The bidirectional carbon flux between pyruvate and oxaloacetate decreased from 36% to 9%. Since the cause of the three different flux states was the allelic exchange in the final L-lysine assembling pathway or the glutamate export activity, respectively, the flexible response is the effect. This shows conclusively the enormous flexibility within the central metabolism of C. glutamicum to supply precursors upon their withdrawal for the synthesis of amino acids. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 168-180, 1997.
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    Quantification of brewers' yeast flocculation in a stirred tank: Effect of physical parameters on flocculation (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 190-200 
    Details
    ISSN: 0006-3592
    Keywords: flocculation ; brewers' yeast ; floc size ; single cells ; light extinction ; sedimentation ; stirred tank ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Quantification of yeast flocculation under defined conditions will help to understand the physical mechanisms of the flocculation process used in beer fermentation. Flocculation was quantified by measuring the size of yeast flocs and the number of single cells. For this purpose, a method to measure floc size and number of single cells in situ was developed. In this way, it was possible to quantify the actual flocculation during fermentation, without influencing flocculation. The effects of three physical parameters, floc strength, fluid shear, and yeast cell concentration, on flocculation during beer fermentation, were examined. Increasing floc strength results in larger flocs and lower numbers of single cells. If the fluid shear is increased, the size of the flocs decreases, and the number of single cells remains constant at approximately 10% of the total cells present. The cell concentration also influences flocculation, a reduction of 50% in cell concentration leads to a decrease of about 25% in floc size. The number of single cells decreases in linear proportion to the cell concentration. This means that, during yeast settling at full scale, the number of single cells decreases. The results of this study are used in a model for yeast flocculation. With respect to full scale fermentation the effect of cell concentration will play an important role, for flocculation and sedimentation will occur simultaneously leading to a quasi steady state between these phenomena. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 190-200, 1997.
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    On-line measurement and analysis of yeast flocculation (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 179-184 
    Details
    ISSN: 0006-3592
    Keywords: flocculation ; on-line measurement ; floc formation rate ; floc dispersion rate ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The ability of yeast to flocculate is important in different separation processes, especially in the beer industry. Because of the regulation purposes, there is a need for online monitoring. With the presented measuring set-up, consisting of a peristaltic pump, a photometer, and a computer, it is possible to determine the onset of flocculation as well as to follow flocculation intensity and the concentration of nonflocculated cells. It was found that for the yeast strain Saccharomyces cerevisiae ZIM 198 the decrease of nonflocculated cells (after flocculation has occurred) during the exponential growth can be described by an exponential equation for the first-order process, whereas the increase of free cells due to dispersion of the flocs during the stationary phase follows the form of the growth curve. It was also demonstrated that the absorbency profiles of yeast sedimentation can be described by the second-order equation suggested by Stradford and Keenan for the decrease of cell concentration during sedimentation. © 1997 John Wiley & Sons, Inc.
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    Production of antioxidant vitamins, β-carotene, vitamin C, and vitamin E, by two-step culture of Euglena gracilis Z (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 185-190 
    Details
    ISSN: 0006-3592
    Keywords: antioxidant vitamins ; vitamin C ; vitamin E ; β-carotene ; Euglena gracilis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Euglena gracilis Z is one of the few microorganisms which simultaneously produces antioxidant vitamins such as β-carotene and vitamins C and E. Photoheterotrophically cultured E. gracilis Z produced larger levels of biomass but with a lower content of antioxidant vitamins than photoautotrophically grown cultures. For efficient production of these vitamins, a two-step culture was performed. Cells were grown photoheterotrophically and then transferred to photoautotrophic conditions. When E. gracilis Z cells were grown in fed-batch culture under photoheterotrophic conditions, their density reached 19 g/L after 145 h. Subsequent transfer of these cells to photoautotrophic conditions increased vitamin content, enhancing the total vitamin yields, which were 71.0 mg/L of β-carotene, 30.1 mg/L of vitamin E, and 86.5 mg/L of vitamin C. © 1997 John Wiley & Sons, Inc.
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    Identification of linearity in the biofilm process and its operational utility (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 253-258 
    Details
    ISSN: 0006-3592
    Keywords: biofilm ; deep biofilm reactor (DBFR) ; kinetics ; linearity ; operational control ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Various reported field studies on the performance of biofilm reactors suggest that the linear control of the system is effective for maintaining the consistent treatment efficiency under changing environmental conditions. However, no theoretical basis is available in the literature to substantiate such a claim. In this article, inherent linearity of the biofilm process has been identified along with the conditions under which this linearity exists. Exploiting the linear state of the system, operational criteria for regulating the performance of the biofilm reactors are obtained. The utility and applicability of the developed criteria are numerically demonstrated. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 253-258, 1997.
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    Performance of a styrene-degrading biofilter containing the yeast Exophiala jeanselmei (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 259-266 
    Details
    ISSN: 0006-3592
    Keywords: waste gas ; styrene ; fungi ; biofilter performance ; biofilm ; Exophiala jeanselmei ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A general mathematical model developed for a description of pollutant degradation in a biofilm was used to evaluate the performance of a biofilter for the purification of styrene-containing gas. The biofilter contained perlite as an inert support on which a biofilm was present composed of a mixed microbial population containing the fungus Exophiala jeanselmei as a major styrene-degrading microorganism. Although styrene is a moderately hydrophobic compound, the biofilter was reaction limited at a styrene gas phase concentration of 0.1-2.4 g/m3. Limitation of biofilter performance by the mass transfer of styrene was only observed at styrene concentrations lower than 0.06 g/m3. A maximal styrene degradation rate of 62 g/(m3 · h) was maintaind for over 1 year. At a high styrene concentration, the maximal styrene degradation rate could be increased to 91 g/(m3 · h) by increasing the oxygen concentration in the gas from 20 to 40%. After 300 days of operation, the dry-weight biomass concentration of the filter bed was 41% (w/w), and an average biofilm thickness of 240-280 μm, but maximal up to 600 μm, was observed. Experimental results and model calculations indicated an effective biofilm thickness of about 80 μm. It is postulated that the thickness of the effective biofilm is determined by the oxygen availability in the biofilm. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 259-266, 1997.
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    Microbial ecosystems in compost and granular activated carbon biofilters (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 296-303 
    Details
    ISSN: 0006-3592
    Keywords: biofilters ; microbial ecocystems ; compost ; granular activated carbon ; phospholipid fatty acid analysis ; POTW ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Compost and granular activated carbon biofilters operated at a wastewater treatment plant simultaneously removed low concentrations of hydrogen sulfide and volatile organic compounds. Through the use of phospholipid fatty acid analyses, the effects of declining pH caused by sulfide oxidation were established for microbial growth, microorganism stress, and microbial community structure. Microorganisms on both media demonstrated increases in microbial densities, varying degrees of environmental stress, and domination by gram-negative bacteria. However, the declining pH had little effect on compound removal, which was greater than 99% for the hydrogen sulfide and greater than 70% for the oxygenated and aromatic hydrocarbons. The microbial communities adjusted to difficult environmental conditions through acclimation of the species present or by growth of low-pH-tolerant species. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 296-303, 1997.
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    Processing and secretion of insulin-related peptides in an insulinoma cell line (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 283-289 
    Details
    ISSN: 0006-3592
    Keywords: regulated secretion ; insulin processing ; insulin secretion ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Certain classes of prohormones and other neuroendocrine or endocrine-derived secretory proteins are post-translationally modified in the secretory storage granules. If such molecules were to be biosynthesized to acceptable quantity and yield using endocrine-derived cell lines, it would be important to understand the relationship between the secretory dynamics and the conversion and release of the immature and mature forms of the molecule. We studied aspects of such a relationship using the endocrine-derived cell line βTC-3, which synthesizes murine proinsulin, sequesters it into secretory granules, and converts it into mature insulin. In T-flask experiments with confluent cultures of βTC-3 cells, intracellular and secreted (pro)insulin was sampled before and after episodes of stimulated exocytosis and recharging and quantified by radioimmunoassay and reversed-phase high-performance liquid chromatography (HPLC). Under conditions of steady-state secretion in glucose-rich growth medium the cells turned over their (pro)insulin inventory (90 ± 5% mature insulin) at 2-3% per hour through secretion of (pro)insulin which was less than 70% mature. During an episode of hyperstimulated exocytosis induced by the combined secretagogues carbachol (1 μM) and isobutylmethylxanthine (1 mM), ∼80% of the intracellular (pro)insulin stores were depleted within 2 h and 84 ± 4% of the secreted (pro)insulin was in the mature form. Following the discharging episode, exocytosis was suppressed to 10% of its steady-state rate with a treatment which attenuated calcium influx (20 μM verapamil with reduced levels of calcium in the medium). Under this condition the secreted protein was only ∼50% converted to mature insulin, but 85 ± 10% of the net (pro)insulin accumulating within the intracellular stores was converted to the mature form. The inverse relationship between rate of secretion and degree of conversion of secreted (pro)insulin is consistent with a previously observed phenomenon of preferential basal secretion from immature secretory granules. This tends to enrich the secreted peptides in immature forms relative to the total intracellular pool. Preferential early secretion can best be overcome by rapid discharging of the long-term and predominantly mature stores. Thus, a cyclic controlled secretion process wherein product is collected during intermittent discharging episodes would provide a better yield of mature product than would steady-state secretion. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 283-289, 1997.
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    Phosphate uptake kinetics by Acinetobacter isolates (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 304-309 
    Details
    ISSN: 0006-3592
    Keywords: biological phosphorus removal ; activated sludge ; phosphate uptake kinetics ; overplus phenomenon ; luxury uptake ; Acinetobacter ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Acinetobacter isolates from activated sludge treatment plants of forest industry were used as model organisms for polyphosphate accumulating bacteria to study excess phosphate uptake by the overplus phenomenon as well as luxury uptake of phosphate during growth. The initial, rapid phosphate uptake by the phosphorus-starved Acinetobacter isolates (the overplus phenomenon) followed the Michaelis-Menten model (maximum initial phosphate uptake rate 29 mg P g-1 dry mass (DM) h-1, half-saturation constant for excess phosphate uptake 17 mg P L-1). During the rapid uptake no growth was observed, but most cells contained polyphosphate granules. Also growth and luxury uptake of phosphate could be modeled with the Michaelis-Menten equation (maximum phosphate uptake rate 3.7-12 mg P g-1 DM h-1, half-saturation constant for growth 0.47-6.0 mg P L-1, maximum specific growth rate 0.15-0.55 h-1). © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 304-309, 1997.
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    Ethanol-type fermentation from carbohydrate in high rate acidogenic reactor (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 54 (1997), S. 428-433 
    Details
    ISSN: 0006-3592
    Keywords: fermentation ; two-stage anaerobic waste treatment ; acidogenic reactor ; fermentation type ; hydrogen partial pressure ; ethanol-type fermentation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: It has been found, in this study, that a new ethanol-type fermentation can be obtained in a continuous flow, high-rate acidogenic reactor receiving molasses as the feed. The operating pH must be maintained at about 4.5 to avoid onset of propionic fermentation. The acidogenic reactor had a VSS level of 20 g/L and its organic loading was as high as 80 to 90 kg COD/m3 d. The operating ORP was around -250 mV. The ethanol-type fermentation was characterized by a simultaneous production of acetic acid and ethanol, while the yield of propionic was minimal even at a high organic loading rate of 80 to 90 kg COD/m3 d, and also, the hydrogen partial pressure was as high as 50 kPa. Thus, this study has shown that the production of propionic acid is not always related to high hydrogen partial pressure. When the operating pH was increased to 5.5, the yield of propionic acid became significant. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 428-433, 1997.
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    On the pH memory of lyophilized compounds containing protein functional groups (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 345-348 
    Details
    ISSN: 0006-3592
    Keywords: fourier transform infrared (FTIR) spectroscopy ; lyophilization ; pKa ; protein ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Lyophilized proteins exhibit “pH memory,” i.e., their behavior in the solid form corresponds to the pH of the aqueous solution from which they were freeze dried. Herein, we directly tested whether the ionization state is “remembered” by model organic compounds containing various protein functional groups (amino, carboxyl, and phenolic). The fraction of ionized species was quantitated from the infrared spectra of both the aqueous and lyophilized states. The pKa values in the aqueous and lyophilized forms for each compound were found to be quite similar, within 0.3 units from each other. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 345-348, 1997.
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    Substrate utilization and mass transfer in an autotrophic biofilm system: Experimental results and numerical simulation (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 363-371 
    Details
    ISSN: 0006-3592
    Keywords: biofilm ; autotrophic bacteria ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An autotrophic biofilm has been investigated for over 10 months in a biofilm tube reactor. The objective of this investigation was the verification and improvement of a biofilm model. The use of a Clark-type oxygen microelectrode in situ allowed the determination of the substrate flux in the biofilm. Also, the population dynamics of the autotrophic bacteria could be evaluated by varying the substrate conditions. Simulation of the experimental results showed that the liquid phase of the biofilm decreased with biofilm depth. This could be described by a logistic function. The density of the inert volume fraction was found to be higher than that of the viable bacteria. This was verified in a nonsubstrate phase of 5 weeks. Growth and decay of the autotrophic bacteria could be described by the growth, endogenous respiration, and death processes. Mass transfer coefficients at the bulk/biofilm interface were evaluated. They were found to be one order of magnitude higher than those known from hydrodynamics in tubes without a biofilm. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 363-371, 1997.
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    Peptide condensation activity of a neutral protease from Vibrio sp. T1800 (Vimelysin) (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 387-390 
    Details
    ISSN: 0006-3592
    Keywords: enzymatic synthesis ; peptide synthesis ; Vibrio ; protease ; thermolysin ; organic solvent ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Condensation of Cbz-Asp and PheOMe catalyzed by a neutral protease from Vibrio sp. T1800 (Vimelysin: VLN) was studied. VLN showed a relatively higher catalytic activity of condensation and an apparently larger yield after 3 h or 24 h, in comparison with thermolysin (TLN), especially at lower pH and temperatures.VLN showed higher solvent-tolerance than TLN. TLhe apparent highest yield (25%) was obtained in 30% DMSO by using VLN; under similar conditions, TLN gave only about a half of this value. The rate of the condensation reaction per mole of enzyme (v/[E]o) in DMSO 50% at 37°C and pH 6.5 was 0.16 s-1 for VLN and 0.047 s-1 for TLN. In 30% ethanol VLN showed more than three-fold peptide yield than TLN after 5 h reaction. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 387-390, 1997.
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    Enzymatic assay of cholesterol by reaction rate measurements (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 391-396 
    Details
    ISSN: 0006-3592
    Keywords: assay ; cholesterol ; cholesterol oxidase ; free and total cholesterol ; cholesterol esterase ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A dynamic method for free and total cholesterol assay based on the oxidation of cholesterol by cholesterol oxidase, and conversion of cholesteryl oleate to cholesterol by cholesterol esterase is discussed in this article. The reaction conditions for total cholesterol assay were a temperature of 310 K and pH of 7.4. For conversion of cholesteryl oleate to cholesterol, the samples were incubated with 0.6 unit/mL of cholesterol esterase and 0.02 g/mL of taurocholate. The determination of initial reaction rates in the oxidation of free cholesterol, which is directly related to the cholesterol concentration, was found to be rapid, reliable, and inexpensive. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 391-396, 1997.
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    Control of heterotrophic layer formation on nitrifying biofilms in a biofilm airlift suspension reactor (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 397-405 
    Details
    ISSN: 0006-3592
    Keywords: airlift reactor ; biofilm ; biofilm detachment ; control biofilm formation ; heterotrophic layer ; hydraulic retention time ; nitrification ; oxygen diffusion limitation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A Biofilm Airlift Suspension (BAS) reactor was operated with nitrifying biofilm growth and heterotrophic suspended growth, simultaneously converting ammonium and acetate. Growth of heterotrophs in suspension decreases the diffusion limitation for the nitrifiers, and enlarges the nitrifying capacity of a biofilm reactor. Neither nitrifiers nor heterotrophs suffer from additional oxygen diffusion limitation when the heterotrophs grow in suspension. Control of the location of heterotrophic growth, either in suspension or in biofilms over the nitrifying biofilms, was possible by manipulation of the hydraulic retention time. A time delay for formation and disappearance of the heterotrophic biofilms of 10 to 15 days was observed. Surprisingly, it was found that in the presence of the heterotrophic layers the maximum specific activity on ammonia of the nitrifying biofilms increased. The reason for the increase in activity is unknown. The effect of heterotrophic biofilm formation on oxygen diffusion limitation for the nitrifiers is discussed. Some phenomena compensating the increased mass transfer resistance due to the growth of a heterotrophic layer are also presented. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 397-405, 1997.
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    Protein denaturation by combined effect of shear and air-liquid interface (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 54 (1997), S. 503-512 
    Details
    ISSN: 0006-3592
    Keywords: aggregation by air-liquid interface ; foaming ; rhDNase ; rhGH ; shear ; shear rate ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The effect of shear alone on the aggregation of recombinant human growth hormone (rhGH) and recombinant human deoxyribonuclease (rhDNase) has been found to be insignificant. This study focused on the synergetic effect of shear and gas-liquid interface on these two model proteins. Two shearing systems, the concentric-cylinder shear device (CCSD) and the rotor/stator homogenizer, were used to generate high shear (〉 106) in aqueous solutions in the presence of air. High shear in the presence of an air-liquid interface had no major effect on rhDNase but caused rhGH to form noncovalent aggregates. rhGH aggregation was induced by the air-liquid interface and was found to increase with increasing protein concentration and the air-liquid interfacial area. The aggregation was irreversible and exhibited a first-order kinetics with respect to the protein concentration and air-liquid interfacial area. Shear and shear rate enhanced the interaction because of its continuous generation of new air-liquid interfaces. In the presence of a surfactant, aggregation could be delayed or prevented depending upon the type and the concentration of the surfactant. The effect of air-liquid interface on proteins at low shear was examined using a nitrogen bubbling method. We found that foaming is very detrimental to rhGH even though the shear involved is low. The use of anti-foaming materials could prevent rhGH aggregation during bubbling. The superior stability exhibited by rhDNase may be linked to the higher surface tension and lower foaming tendency of its aqueous solution. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 503-512, 1997.
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    Cell cycle model to describe animal cell size variation and lag between cell number and biomass dynamics (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 372-379 
    Details
    ISSN: 0006-3592
    Keywords: cell cycle model ; cell size variation ; lag phenomenon ; cell number ; biomass dynamics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The use of cell numbers rather than mass to quantify the size of the biotic phase in animal cell cultures causes several problems. First, the cell size varies with growth conditions, thus yields expressed in terms of cell numbers cannot be used in the normal mass balance sense. Second, experience from microbial systems shows that cell number dynamics lag behind biomass dynamics. This work demonstrates that this lag phenomenon also occurs in animal cell culture. Both the lag phenomenon and the variation in cell size are explained using a simple model of the cell cycle. The basis for the model is that onset of DNA synthesis requires accumulation of G1 cyclins to a prescribed level. This requirement is translated into a requirement for a cell to reach a critical size before commencement of DNA synthesis. A slower growing cell will spend more time in G1 before reaching the critical mass. In contrast, the period between onset of DNA synthesis and mitosis, τB, is fixed. The two parameters in the model, the critical size and τB, were determined from eight steady-state measurements of mean cell size in a continuous hybridoma culture. Using these parameters, it was possible to predict with reasonable accuracy the transient behavior in a separate shift-up culture, i.e., a culture where cells were transferred from a lean environment to a rich environment. The implications for analyzing experimental data for animal cell culture are discussed. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 372-379, 1997.
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    Whey protein fractionation: Isoelectric precipitation of α-lactalbumin under gentle heat treatment (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 391-397 
    Details
    ISSN: 0006-3592
    Keywords: whey ; fractionation ; α-lactalbumin ; citrate ; co-precipitation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The selective precipitation of α-lactalbumin (α-LA) at a pH around its isoelectric point (4.2) under heat treatment is the basis for a fractionation process of whey proteins. In these conditions, β-lactoglobulin remains soluble, whereas bovine serum albumin and immunoglobulins co-precipitate. Knowledge of the mechanism governing the α-LA precipitation influences the choice of operating conditions and enables optimization of the fractionation process. α-LA is a calcium metallo-protein and its isoelectric precipitation is governed by the protein-calcium complexation equilibrium. Citrate, a sequestrant of calcium, decreases the free calcium concentration and displaces the precipitation phenomenon to a lower temperature range. A study of the effect of citrate on the precipitation phenomena of whey proteins is presented. Whatever the citrate content, precipitation curves for bovine serum albumin (BSA) and α-LA intersect at a temperature around 45°C. For a temperature of heat treatment lower than 40°C, a selective enrichment in α-LA of the precipitated phase is observed. As addition of citrate leads to high α-LA precipitated fractions at a temperature around 35°C, the precipitation step may be performed at this temperature. It results in a reduced heat denaturation of whey proteins and in a higher α-LA purity in the precipitated fraction. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 391-397, 1997.
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    Analysis of cell growth in a polymer scaffold using a moving boundary approach (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 422-432 
    Details
    ISSN: 0006-3592
    Keywords: cell growth ; chondrocyte generation ; nutrient consumption ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Two mathematical models of chondrocyte generation and nutrient consumption are developed to analyze the behavior of cell growth in a biodegradable polymer matrix. Substrate reaction and diffusion are analyzed in two regions: one consisting of cells and nutrients and the other consisting of only nutrients. A pseudo-steady state approximation for the transport of nutrients in these two regions is utilized. The rate of growth is determined by a moving boundary equation that equates the rate at which the interfacial region between the cells and the void space moves to a substrate dependent growth reaction. The change in the location of this interfacial region with time therefore depicts the rate at which the cells propagate. The two limiting cases discussed in this article represent extremes in how the cells will grow in the polymer matrix; one case assumes that cells grow inward from the external boundary, and the other case assumes that cells grow parallel to the external boundary. The results of both models are compared to experimental data found in the literature. It is found through these comparisons that the model parameters, including the unit cell spacing parameter L, the metabolic rate constant k, the growth rate constant kG, and external mass transfer coefficient, K, may vary as the thickness of the polymer matrix is changed, however, unrealistic and large changes in the diffusion coefficients were required to account for the full range of experimental data. Furthermore, these results suggest modification of the functional form of the growth kinetics to include substrate or product inhibition, or death terms. Based upon diffusion/reaction concepts, these models for cell growth in a biodegradable polymer give bounds for the upper and lower limits of the cellular growth rate and nutrient consumption in a polymer matrix and will aid in the development of more extensive models. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 422-432, 1997.
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    Production of recombinant human antithrombin III on 20-L bioreactor scale: Correlation of supernatant neuraminidase activity, desialylation, and decrease of biological activity of recombinant glycoprotein (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 441-448 
    Details
    ISSN: 0006-3592
    Keywords: Chinese hamster ovary (CHO) cells ; glycoprotein ; recombinant human antithrombin III (rhAT III) ; neuraminidase activity ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Chinese hamster ovary (CHO) cells producing the recombinant glycoprotein human antithrombin III (rhAT III) were batch cultivated in a 20-L bioreactor for 13 days. Neuraminidase activity in cell-free supernatant was monitored during cultivation and free sialic acid was determined by HPLC. Neu5Acα(2→3)Gal-specific Maackia amurensis and Galβ(1→4)GlcNAc-specific Datura stramonium agglutinin were used for determination of sialylated and desialylated rhAT III, respectively. A commercial test kit was used for evaluation of functional rhAT III activity. Supernatant neuraminidase as well as lactate dehydrogenase activity increased significantly during batch growth. The enhanced number of dead cells correlated with increased neuraminidase activity, which seemed to be principally due to cell lysis, resulting in release of cytosolic neuraminidase. Loss of terminally α(2→3) linked sialic acids of the oligosaccharide portions of rhAT III, analyzed in lectin-based Western blot and lectin-adsorbent assays, correlated with a decrease of activity of rhAT III produced throughout long-term batch cultivation. Thus, structural oligosaccharide integrity as well as the functional activity of recombinant glycoprotein depend on the viability and mortality of the bioreactor culture, and batches with a high number of viable cells are required to guarantee production of glycoproteins with maximum biological activity. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 441-448, 1997.
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    DNA encapsulation by an air-agitated, liquid-liquid mixer (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 464-470 
    Details
    ISSN: 0006-3592
    Keywords: microencapsulation ; microcapsules ; microspheres ; alginate ; emulsification ; DNA ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Smooth and spherical alginate microspheres and nylon-membrane bound microcapsules were formed in an air-agitated, liquid-liquid mixer by emulsification/internal gelation and interfacial polymerization respectively. The mean diameter of the alginate microspheres ranged from 100 to 800 μm, and was controlled by process modifications. Increase in emulsifier concentration, gas flowrate, and emulsification time resulted in smaller microsphere size as did a decrease in liquid height. Increase in the dispersed phase viscosity resulted in a longer emulsification time required for approaching a minimum microsphere size. Microspheres could be formed with the proportion of dispersed phase approaching 30%. The yield of alginate microspheres was 70%, with losses attributed to incomplete recovery during washing and filtration operations. The yield of DNA encapsulation within the fraction of recovered microspheres, was 94%. The small loss was thought to occur by surface release during the washing of the microspheres. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 464-470, 1997.
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    Protein salting-out: Phase equilibria in two-protein systems (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 567-574 
    Details
    ISSN: 0006-3592
    Keywords: salting out ; precipitation ; protein separation ; protein association ; lysozyme ; α-chymotrypsin ; ovalbumin ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The phase behavior of two aqueous binary protein mixtures, lysozyme-chymotrypsin and lysozyme-ovalbumin, was determined in ammonium sulfate solutions. Protein concentrations were determined in both phases as a function of pH and ionic strength. For lysozyme-chymotrypsin mixtures, the observed phase behavior was similar to that for each individual protein; the presence of the second protein had little influence. The phase behavior of lysozyme-ovalbumin mixtures, however, was different from that of the respective single-protein systems. Lysozyme and ovalbumin are found together in egg whites; their association is both pH and ionic-strength dependent. The association of proteins is a key determinant of protein solubility in salt solutions. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 567-574, 1997.
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    Production of a high viscosity polysaccharide, methylan, in a novel bioreactor (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 54 (1997), S. 115-121 
    Details
    ISSN: 0006-3592
    Keywords: Methylobacterium organophilum ; high viscosity polysaccharide ; methylan ; multidisk mixer ; bioreactor ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The effect of shear stress on the production of a high viscosity polysaccharide, methylan, from methanol by Methylobacterium organophilum was investigated by using a multidisk mixer. It was observed in the multidisk mixer with defined shear stresses that the specific production rate of methylan increased gradually with increasing shear stress up to 30 Pa, and the production rate was constant beyond 30 Pa. This result suggested that the limited mass transfer from the medium into cells reduced methylan production. A novel bioreactor that provided the large volume of a high shear region was used to increase methylan production. Fed-batch cultures in the novel bioreactor were performed by the dissolved oxygen-stat method of methanol. When 1.13 g/L ammonium ion was added, the concentrations of cells of methylan were 31 and 20.6 g/L, respectively. The productions of cells and methylan in our designed bioreactor were 20 and 50% higher than those obtained in a conventional fermentor. The methylan content reached a maximum of 20.7 g/L in the bioreactor and the viscosity of the fermentation broth was 127 Pa · s, which corresponds to 68 g/L as a xanthan. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 115-121, 1997.
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    Activity of toluene-degrading Pseudomonas putida in the early growth phase of a biofilm for waste gas treatment (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 54 (1997), S. 131-141 
    Details
    ISSN: 0006-3592
    Keywords: waste gas treatment ; trickling filter ; toluene ; biofilm growth kinetics ; 16S rRNA probes ; Pseudomonas putida ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A biological trickling filter for treatment of toluene-containing waste gas was studied. The overall kinetics of the biofilm growth was followed in the early growth phase. A rapid initial colonization took place during the first three days. The biofilm thickness increased exponentially, whereas the incease of active biomass and polymers was linear. In order to investigate the toluene degradation, various toluene degraders from the multispecies biofilm were isolated, and a Pseudomonas putida was chosen as a representative of the toluene-degrading population. A specific rRNA oligonucleotide probe was used to follow the toluene-degrading P. putida in the multispecies biofilm in the filter by means of number and cellular rRNA content. P. putida appeared to detach from the biofilm during the first three days of growth, after which P. putida was found at a constant level of 10% of the active biomass in the biofilm. Based on the rRNA content, the in situ activity was estimated to be reduced to 20% of cells grown at maximum conditions in batch culture. The toluene degraded by P. putida was estimated to be a minor part (11%) of the overall toluene degradation. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 131-141, 1997.
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    Bidirectional reaction steps in metabolic networks: I. Modeling and simulation of carbon isotope labeling experiments (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 101-117 
    Details
    ISSN: 0006-3592
    Keywords: stationary flux analysis ; metabolite flux balancing ; 13C isotope labeling experiments ; NMR ; metabolic engineering ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The extension of metabolite balancing with carbon labeling experiments, as described by Marx et al. (Biotechnol. Bioeng. 49: 11-29), results in a much more detailed stationary metabolic flux analysis. As opposed to basic metabolite flux balancing alone, this method enables both flux directions of bidirectional reaction steps to be quantitated. However, the mathematical treatment of carbon labeling systems is much more complicated, because it requires the solution of numerous balance equations that are bilinear with respect to fluxes and fractional labeling. In this study, a universal modeling framework is presented for describing the metabolite and carbon atom flux in a metabolic network. Bidirectional reaction steps are extensively treated and their impact on the system's labeling state is investigated. Various kinds of modeling assumptions, as usually made for metabolic fluxes, are expressed by linear constraint equations. A numerical algorithm for the solution of the resulting linear constrained set of nonlinear equations is developed. The numerical stability problems caused by large bidirectional fluxes are solved by a specially developed transformation method. Finally, the simulation of carbon labeling experiments is facilitated by a flexible software tool for network synthesis. An illustrative simulation study on flux identifiability from available flux and labeling measurements in the cyclic pentose phosphate pathway of a recombinant strain of Zymomonas mobilis concludes this contribution. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 101-117, 1997.
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    Effect of serum-free and serum-containing medium on cellular levels of ER-based proteins in various mouse hybridoma cell lines (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 54 (1997), S. 165-180 
    Details
    ISSN: 0006-3592
    Keywords: monoclonal antibody ; hybridoma ; BiP ; PDI ; GRP94 ; serum-free medium ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: BiP, GRP94 and PDI, three endoplasmic reticulum (ER) based proteins are involved in the maturation of secretory proteins and might represent a bottleneck in the secretory pathway of monoclonal antibodies (MAB). With the three hybridoma cell lines tested, MAB production kinetics were significantly increased for the batch cultures done in serum-free medium (SFM) with respect to those done in serum-containing medium (SCM). It could be established that there was a correlation between the cellular levels of PDI and GRP94 and the specific MAB production rate. With respect to BiP, no correlation with the MAB production rate was observed. The non-producing myeloma cell line X63, used as a reference, showed increased cellular PDI levels when cultivated in SFM. However, in this cell, the cellular GRP94 levels were not significantly influenced by the medium composition.It was concluded that SFM induced an increase of cellular PDI levels and this elevation seemed to be responsible for the increase in the specific MAB production rates. On the other hand, only MAB producing cells showed an increase in the cellular GRP94 levels which might be a result of increased MAB sythesis. Indeed, I.13.17 cultivated in SFM supplemented with serum showed a significantly reduced (about 50%) specific MAB production rate in comparison to I.13.17 cultivated in non-serum supplemented SFM. The cellular PDI and BiP levels did not vary between these conditions of culture, whereas the cellular GRP94 level was about two-fold lower in I.13.17 cultivated in SFM when supplemented with serum than in I.13.17 cultivated in SFM without futher supplementation. These results are discussed with respect to the medium composition as well as in the context of apparent and potential bottlenecks within the secretory pathway of MAB. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 165-180, 1997.
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    Selection of salt hydrate pairs for use in water control in enzyme catalysis in organic solvents (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 367-374 
    Details
    ISSN: 0006-3592
    Keywords: salt hydrates ; water activity ; subtilisin ; lipase ; organic solvents ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The water activities (aw) of 13 salt hydrate pairs were determined from vapor pressure measurements; aw values for a subset were also estimated from a study of water transfer to isopropylether. The application of salt hydrates as water buffers was investigated in two models: (i) effect of hydration on the initial rate of subtilisincatalyzed transesterification of the nitrophenol ester of CBZ-alanine with butanol; and (ii) effect of hydrates on the equilibrium concentrations of reactants in the esterification of dodecanol and decanoic acid, catalyzed by lipase. Transfer of ions from salt to enzyme particles was also demonstrated. The implications of the results for the successful use of salt hydrates as water buffers are discussed. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 367-374, 1997.
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    Biodegradation of paint stripper solvents in a modified gas lift loop bioreactor (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 163-169 
    Details
    ISSN: 0006-3592
    Keywords: bioreactor ; paint stripper solvents ; biodegradation ; model ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Paint stripping wastes generated during the decontamination and decommissioning of former nuclear facilities contain paint stripping organics (dichloromethane, 2-propanol, and methanol) and bulk materials containing paint pigments. It is desirable to degrade the organic residues as part of an integrated chemical-biological treatment system. We have developed a modified gas lift loop bioreactor employing a defined consortium of Rhodococcus rhodochrous strain OFS and Hyphomicrobium sp. DM-2 that degrades paint stripper organics. Mass transfer coefficients and kinetic constants for biodegradation in the system were determined. It was found that transfer of organic substrates from surrogate waste into the air and further into the liquid medium in the bioreactor were rapid processes, occurring within minutes. Monod kinetics was employed to model the biodegradation of paint stripping organics. Analysis of the bioreactor process was accomplished with BIOLAB, a mathematical code that simulates coupled mass transfer and biodegradation processes. This code was used to fit experimental data to Monod kinetics and to determine kinetic parameters. The BIOLAB code was also employed to compare activities in the bioreactor of individual microbial cultures to the activities of combined cultures in the bioreactor. This code is of benefit for further optimization and scale-up of the bioreactor for treatment of paint stripping and other volatile organic wastes in bulk materials. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 163-169, 1997.
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    Abrasion of suspended biofilm pellets in airlift reactors: Effect of particle size (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 206-215 
    Details
    ISSN: 0006-3592
    Keywords: biofilm detachment ; abrasion ; collisions ; particle size ; airlift-reactor ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The detachment of biomass from suspended biofilm pellets in three-phase internal loop airlift reactors was investigated under non-growth conditions, and in the presence of bare carrier particles. In the experiments the size of biofilm pellets and bare carrier particles was varied. Results show that an increase in particle size drastically increases the abrasion rate caused by particle collisions. This increase is larger than predicted by conventional collision theory, which accounts for changes in collision frequency and collision impact. However, collision theory was formulated for neutrally buoyant particles which follow the liquid flow. This condition does not hold for biofilm pellets and carrier particles. The difference might therefore be caused by differences in particle responses to flow fluctuations. An empirical relationship, including this flow response, was formulated. The collision impact is also strongly affected by the roughness of a bare carrier particle: sharp and edgy particles cause much more damage than smoother ones. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 206-215, 1997.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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