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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 44 (1994), S. 523-528 
    ISSN: 0006-3592
    Keywords: whey proteins ; proteases ; enzymatic hydrolysis ; peptides ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: We have studied the enzymatic hydrolysis of whey proteins at pH 8 and50°C with two proteases of bacterial origin, MKC Protease 660 L, and one of animal origin, PEM 2500 S. Our results show that a greater degree of hydrolysis is achieved under the same experimental conditions with the bacterial proteases than with the animal one. In our interpretation of the results we propose a mechanism in which the hydrolytic reaction is a zero-order one for the substrate, and the enzyme denaturalizes simultaneously via a second-order kinetic process due to free enzyme attacking enzyme bound to the substrate. Our results also indicate that there is an irreversible serine-protease inhibitor in whey proteins. © 1994 John Wiley & Sons, Inc.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 44 (1994), S. 529-532 
    ISSN: 0006-3592
    Keywords: whey proteins ; proteases ; enzymatic hydrolysis ; peptides ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Using high-pressure liquid chromatography we studied the distribution of molecular weights in whey-protein hydrolysates using the following commercially obtained proteases: Alcalasa 0.6 L and Protease 660 L, both bacterial in origin, and PEM 2500 S, of animal origin. In each of the systems, the range of molecular weights in the hydrolysate depended solely on the degree of hydrolysis (DH) achieved. For DH ≥ 20, between 65% and 95% of the hydrolysate is made up of peptides with a molecular weight of less than 1,000 Da. © 1994 John Wiley & Sons, Inc.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 42 (1993), S. 1-10 
    ISSN: 0006-3592
    Keywords: mycelial kinetics ; symmetric branching tree ; microscopic parameters ; macroscopic parameters ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A mathematical model, linking microscopic to macroscopic parameters of the kinetics of mycelial growth is presented. The model consists of two parts: (a) a microscopic description, based on the assumption that growth of a mycelium can be represented approximately by the growth of a symmetric binary tree, where the branching level (microscopic state variable) is logarithmically related to the number of tips and segments; and (b) a macroscopic description which makes use of the microscopic description in order to define the parameters related to the evolution of biomass (macroscopic state variable) as a function of time. The latter uses a distribution of arrested tips in a population of mycelia, in order to estimate the fraction of non-growing biomass in terms of a power law function with coefficient, n, of the biomass concentration. The microscopic description explains the fact that the germ tube specific growth rate of Aspergillus nidulans measured in a growth chamber, is about the double the specific growth rate of this organism, when measured in shake flasks. It predicts that the length of the hyphal growth unit of the mycelium of Geotrichum candidum would be approximately the double the germ tube length measured at the time just before the first branching event. It also allows the derivation of useful expressions for predicting macroscopic parameters, such as the maximal specific growth rate, the initial amount of biomass, and the amount of biomass before the branching process starts. Those estimates are done in terms of microscopic quantities, i.e., the amount of germinated spores, the diameters of the spores and hyphae, the average rate of tip extension, and the average internodal segment length. Estimation of coefficient n by fitting the macroscopic description to a growth curve of A. niger gives an indication on the degree of skewness of the distribution of arrested mycelia. Estimated macroscopic parameters are in relative good agreement with measured average segment length. © 1993 John Wiley & Sons, Inc.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 50 (1996), S. 700-708 
    ISSN: 0006-3592
    Keywords: α-chymotrypsin ; organic media ; tripeptide synthesis ; CCK-8 ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The enzymatic synthesis of the tripeptide derivative Z-Gly-Trp-Met-OEt is reported. This tripeptide is a fragment of the cholecystokinin C-terminal octapeptide CCK-8. Studies on the α-chymotrypsin catalyzed coupling reaction between Z-Gly-Trp-R1 and Met-R2 have focused on low water content media, using deposited enzyme on inert supports such as Celite and polyamide. The effect of additives (polar organic solvents), the acyl-donor ester structure, the C-α protecting group of the nucleophile, enzyme loading, and substrate concentration were tested. The best reaction medium found was acetonitrile containing buffer (0.5%, v/v) and triethylamine (0.5%, v/v) using the enzyme deposited on Celite as catalyst (8 mg of α-chymotrypsin/g of Celite). A reaction yield of 81% was obtained with Z-Gly-Trp-OCam as acyl donor, at an initial concentration of 80 mM. The tripeptide synthesis was scaled up to the production of 2 g of pure tripeptide with an overall yield of 71%, including reaction and purification steps. © 1996 John Wiley & Sons, Inc.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 287-294 
    ISSN: 0006-3592
    Keywords: specific growth rate ; hyphal morphometry ; Aspergillus niger ; surface growth kinetics ; glucose effect ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Development of surface grown cultures of Aspergillus niger no. 10 was studied at two experimental levels: (a) following the time course of the biomass density (X [=] mg cm-2) and fitting the data by the logistic expression, which yielded a macroscopic specific growth rate expressed as μobs = (dX/Xdt)[1-(X/Xmax)]-1; and (b) measuring morphometric parameters like the specific elongation rate (k) of the germ tubes and their diameters (Dh), the colony rate of radial extension (ur), and the mean length of distal hyphae (Lav) to estimate the specific growth rate with the following proposed expression: μcalc = urln2[Lavln(Lav/Dh)]-1. Increases in the initial glucose concentration (10, 40, 70, 120, 200, and 300 g L-1) caused reductions in the specific growth rates, the elongation kinetics of the germ tubes, and the hyphal diameter, nevertheless, ur and Xmax presented parabolic behavior, showing their maxima in the interval of 90 to 120 g L-1 of glucose. The overall macroscopic effect of the tested concentrations of glucose on surface grown cultures of A. niger was to produce densely packed and slowly extending colonies, where changes in hyphal lengths and diameters were significant. There was good agreement between μobs and μcalc values. Hence, this work validates a kinetic model based on morphometric data to estimate the specific growth rate of molds, obtained from dry weight data, using mold cultures grown in the same solid medium i.e., agar plates. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 287-294, 1997.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 497-506 
    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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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 59 (1998), S. 122-127 
    ISSN: 0006-3592
    Keywords: lipase ; organic solvent ; flavour esters ; interfacial activation ; enzyme conformers ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In order to improve the lipase-catalyzed synthesis of flavour esters, we have used the reported strategy of interfacial activation-based molecular (bio)imprinting [Mingarro et al. 1995. Proc. Natl. Acad. Sci. U.S.A. 92: 3308], later called trapping in the presence of amphiphile interfaces (TPI) [Mingarro et al. 1996. Biochemistry 35: 9935]. Five lipases of fungal and mammalian origin typically used for esterification process have been explored to improve production by TPI treatment. A marked enhancement of enzymatic activity has been observed in all TPI-treated lipases assayed and the activation factor obtained was up to 90-fold. The dependence on chain length of acyl donors in the esterification of geranyl alcohol has been investigated, showing clear differences between activated and nonactivated lipase. The results indicate that this rational approach leads to conversion yields that are remarkably higher, not only than its counterpart pH-optimized control lipase, but also the “protected” lipase by conventional methods (lyoprotectans or salts). We propose this strategy as a promising tool to be used in more industrial biotransformations. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 59:122-127, 1998.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 49 (1996), S. 247-258 
    ISSN: 0006-3592
    Keywords: citric acid ; Aspergillus niger ; linear programming ; carbohydrate metabolism ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The metabolic pathway and the properties of many of the enzymes involved in the citric acid biosynthesis in the mold Aspergillus niger are well known. This fact, together with the availability of new theoretical frameworks aimed at quantitative analyses of control and dynamics in metabolic systems, has allowed us to construct a mathematical model of the carbohydrate metabolism in Aspergillus niger under conditions of citric acid accumulation. The model makes use of the S-system representation of biochemical systems, which renders it possible to use linear programming to optimize the process. It was found that maintaining the metabolite pools within narrow physiological limits (20% around the basal steady-state level) and allowing the enzyme concentrations to vary within a range of 0.1 to 50 times their basal values it is possible to triple the glycolytic flux while maintaining 100% yield of substrate transformation. To achieve these improvements it is necessary to modulate seven or more enzymes simultaneously. Although this seems difficult to implement at present, the results are useful because they indicate what the theoretical limits are and because they suggest several alternative strategies. © 1996 John Wiley & Sons, Inc.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 456-463 
    ISSN: 0006-3592
    Keywords: enzymatic fragment condensation ; α-chymotrypsin ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The kinetically controlled condensation reaction of Z-Gly-Trp-Met-OR1 (R1: Et, Al, Cam) and H-Asp-(OR2)-Phe-NH2 (R2: H, But) catalyzed by α-chymotrypsin deposited onto polyamide in organic media was studied. The effect of the drying process of the enzyme-support preparation, substrate concentrations, reaction medium, acyl donor, and nucleophile structure on both enzymatic activity and pentapeptide yield was investigated. The immobilized preparation directly equilibrated at aw = 0.113, gave higher enzymatic activities than dried with vacuum first, and then equilibrated at aw = 0.113. The addition of triethylamine to the reaction medium increased dramatically the enzymatic activity. However, the pentapeptide yield was affected neither by the drying procedure nor by the addition of triethylamine. The donor ester Z-Gly-Trp-Met-OAl gave initial reaction rates 2.6 times higher than the conventional ethyl ester derivative but rendered similar yields. The best results were obtained using Z-Gly-Trp-Met-OCam as acyl-donor ester; 80% yield and initial reaction rates 4 times higher than the ethyl ester derivative. In all cases, acetonitrile containing Tris-HCl 50 mM pH 9 buffer (0.5% v/v) and triethylamine (0.5% v/v) was found to be the best reaction system. Under these conditions, it was possible to use the nucleophile H-Asp-Phe-NH2 with β-unprotected aspartic acid residue. In this case, 50% yield was obtained, but economic considerations could lead to select it as nucleophile. Finally, the fragment condensation reaction was carried out at gram scale, obtaining a 39% yield which included the reaction, removal of protecting groups and purification steps. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 456-463, 1997.
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