摘要:

AbstractMolecular‐level mathematical models have been used to evaluate the effectiveness of eight different configurations of repressor synthesis control on the regulation of cloned gene expression initiated from a promoter‐operator sequence. Both single and dual‐repressor situations were considered, employing genetically structured models for thelacand λPRpromoter‐operators in example calculations. Simulation results suggest that the most effective mode of cloned gene expression control is a cross‐regulation configuration carried on a multicopy plasmid. This system was able to control cloned gene transcription in the uninduced state over a broad range of plasmid copy number and also provided the highest overall transcription rate in the induced state. The general strategies suggested by these simulations should be applicable for other repressor‐operator‐promoter systems in

ISSN:0006-3592    

DOI:10.1002/bit.260380702

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractAn experimental study of permeation of dilute BSA solutions (filtration) at microfiltration membranes has been carried out. Most measurements were made with capillary pore aluminum oxide membranes, with some comparative measurements with tortuous and capillary pore polymeric membranes. In all cases, a continuous and substantial decrease in the rate of permeation with time was observed. This decrease in permeation with time was observed. This decrease in permeation rate was due neither to concentration polarization nor to protein adsorption alone. However, it could be quantified using the standard blocking filtration law, which describes a decrease in pore volume due to deposition of protein on the walls of the pore. The maximum calculated thickness of the deposited layers was 55nm on the walls of 200‐nm diameter pores. This phenomenon is quite different to adsorption of protein at such surfaces, this latter giving only sub‐monolayer or monolayer protein coverage under the conditions stud

ISSN:0006-3592    

DOI:10.1002/bit.260380703

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractIn this article, we provide a rigorous thermodynamic analysis of microbial growth process, clarify the role of the generalized degree of reduction concept as it is used in both stoichiometric equations and as a characterizing factor for thermophysical properties, and introduce a classification method to account for errors when using the generalized degree of reduction to estimate the energy and free energy contents of molecules. We maintain the advantages of using the generalized degree of reduction while correcting for the large errors in the principle of energy regularity, especially for small molecules and for nitrogen‐source compounds. As a result, we obtain more accurate energy balances (heat loads) and second law constraints, and are able to clarify contradictory statements in the literature as to whether nonphotosynthesis fermentation process can produce oxygen or absorb rather than produce heat. Indeed, the answers to such questions become evident using the classification system introduced her

ISSN:0006-3592    

DOI:10.1002/bit.260380704

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractPrior work has demonstrated that the microsin antibiotics are produced by enteric bacteria when the growth medium is depleted of nutrients. Because the control loci could have biotechnical potential, and general stress‐response phenomena are of importance to understanding how bacteria survive in natural and bioreactor environments, we examined further the growth rate dependence of gene expression under the control of the microsin B17 promoter. This work entailed performing batch and chemostat growth experiments with a strain ofE. coliK‐12 containing amcbA‐lacZgene fusion in the chromosome. Our results indicate that when a culture is presented with excess respiratory substrate, a well defined growth rate exists, below which a significant induction event occurs. However, cultures that are fermenting or highly glycolytic tend to express poorly. Additionally, the utility of the fusion strain was examined by performing fed‐batch cultivation experiments. We found that sustained production in a fed‐batch reactor can be accomplished by using a straightforward, exponential nutrient feedin

ISSN:0006-3592    

DOI:10.1002/bit.260380705

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe aptitude of a hollow‐fiber membrane reactor to determine lipase kinetics was investigated using the hydrolysis of triacetin catalyzed by lipase fromCanadida cylindraceaas a model system. The binding of the lipase to the membrane appears not to be very specific (surface adsorption), and probably its conformation is hardly altered by immobilization, resulting in an activity comparable to that of the enzyme in its native form. The reaction kinetics defined on the membrane surface area were found to obey Michaelis‐Menten kinetics. The specific activity of the lipase in the membrane reactor was found to be significantly higher than in an emulsion reactor. The activity and stability of the enzyme immobilized on a hydrophilic membrane surface seem not to be influenced significantly by the choice of the membrane material. The hollow‐fiber membrane reactor is a suitable tool to assess lipase kinetics in a fast and convenien

ISSN:0006-3592    

DOI:10.1002/bit.260380706

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe steady‐state metabolic parameters for a murine hybridoma cell line have been determined in continuous suspension culture over a wide range of dilution rates. Long‐term adaption occurred over seven months in culture and resulted in lower glucose consumption rates, reduced lactate production, higher cell viability, and, consequently, growth rates more nearly matching the dilution rate. Antibody production rates decreased over the first two months and then remained stable for at least 75 days. The antibody production rate was not found to be growth associated. Steadystate amino acid uptake rates are presented for a wide range of growth ra

ISSN:0006-3592    

DOI:10.1002/bit.260380707

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractWe Propose a kinetic expression which accounts for the temperature dependence of ethanol yield losses in batch alcoholic fermentation. Moreover, the characteristic parameters of the microbial growth equation have been calculated forSaccharomyces cerevisiaeunder typical wine industry conditions. A substrate consumption equation is established which minimizes possible model deviations in the latter process stages. Experimental data were obtained in the laboratory and the proposed equations were then applied at an industrial level (2.5 × 104L) where they described the data well

ISSN:0006-3592    

DOI:10.1002/bit.260380708

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe dynamics of chemically induced chloramphenicolaceyl‐transferase (CAT) expression are determined in batch cultures ofEscherichia coliDH5αF'IQ [pKK262‐1]. This article is directed towards understanding the coupling of induced cloned‐protein synthesis and reduced cell growth which are balanced in the optimal system. Experimental results indicate that the best inducer (IPTG) concentration is near 1.0 mMwhen added during midexponential growth. Lower concentrations cause only weak induction, whereas higher concentrations cause sufficiently strong induction that cell growth is suppressed. Induction at the onset of the stationary phase results in high expression but is accompanied by stimulated protease activity. Also, cell mass yield is adversely affected by enhanced protein synthesis. A structured metabolic model is shown to predict the responses of instantaneous growth rate and productivity which result from protein overexpression. This model can be employed to predict alternative reactor strategies and operating conditions necessary for the design of efficient biop

ISSN:0006-3592    

DOI:10.1002/bit.260380709

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractA theoretical model for the lipase‐catalyzed hydrolysis of high‐concentration olive in biphasic isooctane‐aqueous systems has been proposed and confirmed by experiments. The enzymatic reaction of the Michaelis‐Menten type that occurred at the interface between organic and aqueous phases was assumed in deriving the rate equations, from which the maximum reaction rate could be obtained by carefully adjusting the volume ratio between the two phases to the optimal value. Equilibrium conversions higher than 98% for 0.1 g/L olive oil in isooctane were attained for systems with volume ratios up to one. Fractions of lipase and lipase‐substrate complex adsorbed at the interface increased and seemed to approach to asymptotic values asthe rotation speed of impeller increased. Activity of the lipase showed no apparent change between 26 and 37°C, but decrease rapidly with temperature above 43°C. The methodology presented in this work might be used to find kinetic parameters for reactor design

ISSN:0006-3592    

DOI:10.1002/bit.260380710

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractA three compartment model (ER → Golgi → extracellular medium) is used here to describe the interorganelle transport and final secretion of an IgG2amonoclonal antibody (MAb) in 9.2.27 murine hybridoma cells. Model simulations of pulse‐chase and continuous labeling experiments are used to gain a better understanding of the kinetics of MAb interorganelle traffic. Simulation results for the continuous labeling case compare well with experimental data obtained during continuous labeling of 9.2.27 hybridoma cells. Incorporation of this compartmental transport model into our previously developed model of MAb synthesis and assembly can provide a useful tool for analyzing the dynamics and regulation of the complete antibody secretory pathway under different growth and/or nutritional condi

ISSN:0006-3592    

DOI:10.1002/bit.260380711

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY