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  • 1
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 1779-1790 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The kinetics of protein aggregation in salt-induced precipitation processes were studied as a function of salt type, salt concentration, temperature and protein concentration. α-chymotrypsin (αCT) was used as a model protein. Stopped-flow turbidimetry was used to monitor the progress of precipitations. Analysis of the linear portions of the turbidity trajectories indicates that temperature and salt concentration effects are related to protein solubility; the protein concentration dependence is well described by the Smoluchowski collision equation. The aggregation kinetics of partially-inhibited αCT exhibit poisoning behavior, underscoring the importance of dimerization and monomer addition in the precipitation of αCT. Solute particle radius distributions determined via dynamic laser light scattering for low salt and supernatant αCT solutions indicated that significant aggregation does not occur in the absence of supersaturation. A detailed population balance model was proposed that accounted for specific and nonspecific interactions and monomer addition. The model is expected to find general application to protein aggregation phenomena, in particular for proteins that have specific quaternary interactions.
    Additional Material: 6 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 27 (1985), S. 1668-1674 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Plasmid-host cell interactions have been investigated experimentally using Escherichia coli HB101, plasmid RSF1050 which contains the origin of replication of pMB1, and four other closely related copy number mutant plasmids. Growth characteristics of these recombinant strains and β-lactamase activity expressed from a plasmid gene were investigated in Luria broth (LB) and in minimal medium (M9) containing in some cases casamino acids or different concentrations of α-methylglucoside, a competitive inhibitor of glucose transport. Maximum specific growth rates in LB and minimal media were reduced for increasing plasmid content per cell. Plasmid copy number increased when specific growth rate was reduced by changing medium composition. Growth rates of high copy number strains were less sensitive to α-methylglucoside than lower copy number strains and the plasmidfree host. The overall efficiency of plasmid gene expression, measured as the ratio of β-lactamase specific activity to plasmid content, decreased significantly with increasing plasmid content in LB medium.
    Additional Material: 5 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 27 (1985), S. 1699-1709 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A mathematical model has been formulated for product formation by unstable recombinant organisms in batch and in continuous flow reactors. The cell population is characterized by three different genotypes according to the absence or presence of plasmids (segregational instability) and of active cloned gene (structural instability). Empirical growth inhibition factors due to plasmids and to product protein are assigned to the corresponding strains. Product formation kinetics are based upon a quasi-steady-state transcription-translation expression model. An approximate form of these mechanism-based product formation kinetics is identical to the traditional, empirically based Leudeking-Piret formula. Alternative models which consider inhibition based on overall product concentration and based on intracellular product concentration are posed, and their implications are compared. Simulation results based on these models indicate (1) overall plasmid stability depends on product expression and reactor operating conditions as well as on intrinsic segregation and mutation rate parameters; (2) there exists an optimum combination of plasmid copy number and cloned-gene transcription and translation efficiencies to maximize reactor productivity; and (3) continuous reactor dilution rate influences the fraction of productive cells. General trends and substrate, product, and cell concentration time trajectories obtained from model simulation agree well qualitatively with currently available experimental information.
    Additional Material: 8 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 28 (1986), S. 73-87 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The kinetic properties of Saccharomyces cerevisiae immobilized on crosslinked gelatin were found to be substantially different from those of the suspended yeast. Batch fermentation experiments conducted in a gradientless reaction system allowed comparison of immobilized cell and suspended cell performance. The specific rate of ethanol production by the immobilized cell was 40-50% greater than for the suspended yeast. The immobilized cells consumed glucose twice as fast as the suspended cells, but their specific growth rate was reduced by 45%. Yields of biomass from the immobilized cell population were lower at one-third the value for the suspended cells. Cellular composition was also affected by immobilization. Measurements of intracellular polysaccharide levels showed that the immobilized yeast stored larger quantities of reserve carbohydrates and contained more structural polysaccharide than did suspended cells. Flow cytometry was used to obtain. DNA, RNA, and protein frequency functions for immobilized and suspended cell populations. These data showed that the immobilized cells have higher ploidy than cells in suspension. The observed changes in immobilized cell metabolism and composition may have arisen from disturbance to the yeast cell cycle by the cell attachment, causing alterations in the normal pattern of yeast bud development, DNA replication, and synthesis of cell wall components.
    Additional Material: 10 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 28 (1986), S. 1672-1689 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A structured mathematical model for cellular metabolism in Escherichia coli has been extended to encompass the mechanistic structure surrounding the kinetics and control of transcription and translation. The dependence of transcription on RNA polymerase and the mechanism of translation initiation have been explicitly included. This model correctly simulates cell growth, cell composition, and the timing of chromosome synthesis as a function of extracellular substrate concentration for glucose-limited balanced growth. Simulation results for the subpopulation of RNA polymerase engaged in transcription and for the distribution of this subpopulation among different promoter sites agree closely with experimental findings, as do calculated estimates of the active ribosomal fraction. In addition, the existence of an antitermination system for transcription of stable RNA operons is supported by model results. This model should provide a useful framework for investigating metabolic perturbations to E. coli, such as those resulting from insertion of extra-chromosomal vectors into the cells.
    Additional Material: 9 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 30 (1987), S. 297-305 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The relationship between cell mass and cell number dynamics for bacteria such as Escherichia coli depends on the cell cycle parameters C and D. Effects of plasmid copy number on these cell cycle parameters have been studied for Escherichia coli HB101 containing pMB1 plasmids propagated at different copy numbers ranging from 12 to 122. Determination of cell cycle and cell size parameters was accomplished using flow cytometry data on single-cell light scattering and DNA content frequency functions in conjunction with a mathematical model of cell population statistics. Two independent methods for estimating C and D intervals based on flow cytometry were developed and applied with essentially identical results. The presence of plasmids decreases the C and D periods, mean cell sizes, and initiation masses for chromosome replication by 14, 24, 38, and 18%, respectively, relative to corresponding values for plasmid-free host cells. Plasmid copy number has a negligible influence on these parameters, suggesting that host-plasmid inter actions which determine these properties are centered on the single plasmid selected for replication according to the random selection model established for ColE1-type plasmids.
    Additional Material: 6 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 32 (1988), S. 1138-1152 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A systematic procedure has been formulated for estimating the relative intracellular concentrations of sugar phosphates in Saccharomyces cerevisiae based upon 31P nuclear magnetic resonance (NMR) measurements. The sugar phosphate region of the 31P NMR spectrum is first decomposed by computer analysis, and the decomposition consistency and identification of individual sugar phosphate resonances are established based on in vitro chemical shift calibrations determined in separate experiments. Numerous evaluations of intracellular S. cerevisiae compositions for different strains and different cell environments provide the basis for in vivocorrelations of inorganic phosphate chemical shift with the chemical shifts of 3-phosphoglycerate, beta;-fructose 1,6-diphosphate, fructose 6-phosphate, and glucose 6 phosphate. Relative intracellular sugar phosphate concentrations are obtained by correcting peak areas for partial saturation during transient in vivo experiments. In vivo concentrations estimated by this method agree well with estimates for similar systems based on other techniques. This approach does not require costly la belled compounds, and has the advantage that other important metabolic state variables such-as internal and external pH and intracellular levels of phosphate, ATP, ADP, NAD(H), and polyphosphate may be determined from the same 31P spectrum. Extension of this strategy to other cellular systems should be straightforward.
    Additional Material: 12 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 28 (1986), S. 741-746 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 4 Tab.
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  • 9
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A mechanistically detailed single-cell model E. coli B/r-A was adapted to simulate the effects of vector presence on cell metabolism. Competition for RNA polymerase between chromosome and plasmid DNA is explicitly included. Distribution of active ribosomes among chromosome- and plasmid-derived messenger RNA, another key facet of host-plasmid interactions, is also treated in detail. Simulations of recombinant cell growth rate and cloned-gene productivity as a function of relative plasmid number per cell agree closely with experimental results. Model prediction of the variation of cell cycle parameters C and D with plasmid number are roughly consistent with available data. Models of this class can be used to simulate changes in productivity resulting from specific alterations in the expression vector. The effects of changing cloned-gene promoter and ribosome binding strengths and of augmenting cell transcription or translation capacity have been studied using the recombinant cell model. Results suggest that cloned-gene expression is limited by cellular transcription capacity. These and other parametric studies, conveniently implemented using the computer cell, provide important guidance for future experiments directed at better understanding of host-plasmid interactions and at optimizing recombinant system productivity.
    Additional Material: 2 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 34 (1989), S. 825-837 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The bioconversion activity of calcium alginate-immobilized Clostridium acetobutylicum ATCC 824 was investigated in a continuous reactor system utilizing a defined feed medium which did not support cell growth. The changes in biocatalytic activity with time were studied at different pH values as well as when different metabolites (butyric, acetic, and acetoacetic acids) were present in the feed stream. Although the nongrowing cells were metabolically active, the product distribution was shifted from solvent production to acidogenesis. Overall activity losses occurred due to cell lysis, sporulation, and the effects of nitrogen level on macromolecular turnover. These effects were minimized under some operating conditions (e.g., pH 6), resulting in significantly longer productivity lifetimes.
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