摘要:

AbstractA correlation for predicting the diffusion coefficients of proteins at standard conditions is proposed by adapting the Stokes‐Einstein equation to a model for the equivalent hydrodynamic sphere. The radius of gyration, which accounts for the size and shape of protein molecules in solution, was used in deriving the new correlation. The correlation successfully predicted the diffusion coefficients of proteins, for which experimental data were available, with a higher degree of accuracy than achieved by previous correlation method

ISSN:0006-3592    

DOI:10.1002/bit.260350402

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

年代:1990

数据来源: WILEY

摘要:

AbstractIn order to develop a large‐scale fermentation process for the production of human proinsulin in yeast, the intra‐cellular expression of a human superoxide dismutase‐human proinsulin fusion product (SOD‐PI) has been studied. The expression of SOD‐PI inSaccharomyces cerevisiaeis regulated by a hybrid alcohol dehydrogenase 2/glyceraldehyde‐3‐phosphate dehydrogenase promoter. The promoter is repressed by glucose and derepressed by depletion of glucose. Although the genetic stability of the construction is shown to be poor under product‐inducing conditions, it is demonstrated in shake flask experiments that a stable expression potential can be maintained in a complex medium for more than 60 generations by maintaining excess glucose throughout the cultivations. These results have been confirmed in continuous cultures in chemostat and turbidostat experiments. Addition of the glucose analogs glucosamine, 2‐desoxyglucose, methylglucose, and thioglucose also leads to repression of SOD‐PI formation. The analogs, however, are not suitable for improving genetic stability during propagation because of growth inhibition. In batch fermentation experiments in a complex medium at 30°C, it has been demonstrated that initial glucose concentrations up to 50 g/L result in high specific SOD‐PI yields giving an overall yield of up to 700 mg SOD‐PI/L whereas higher glucose concentrations lead to both lower specific and overall yields due to depletion of critical medium components in the production period. In fed‐batch experiments at 30°C it has been possible to obtain high specific SOD‐PI yields even at high biomass concentrations by feeding glucose at a constant rate of 1.5 g/L/h for 40 h followed by a feeding of ethanol at 1.0 g/L/h for 24 h, thus giving an overall yield of 1200 mg/L. Decreasing the temperature from 30 to 26°C leads to improved yields in batch as well as fed‐batch experiments. The optimized fed‐batch fermentation process which is suitable to be scaled up to the cubic meter level has been tested in 200‐L fermentations resulting in yields of more than 1500 mg/L of the fusion protein which conveniently can be used as a precursor in the produc

ISSN:0006-3592    

DOI:10.1002/bit.260350403

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

年代:1990

数据来源: WILEY

摘要:

AbstractIt is shown that, in a mixed culture, under realistic assumptions, the optimal temperature profile maximizing the final biomass production under the constraint of the final relative proportions of the two populations is constant. This result is illustrated with a simulation experiment on a lactic fermentation model.

ISSN:0006-3592    

DOI:10.1002/bit.260350404

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

年代:1990

数据来源: WILEY

摘要:

AbstractA model was formulated to examine specific experimental data of growth and heterologous product formation with recombinantSaccharomyces cerevisiaewhile incorporating available literature. The model simulated dry cell weight, glucose, ethanol, dissolved oxygen, human Epidermal Growth Factor (hEGF) production, fraction of recombinant cells, oxygen uptake rate, and carbon dioxide production rate for batch, fed batch, and hollow fiber bioreactor configurations. Nineteen differential equations, 24 analytical equations, and 48 parameters were required. Due to the lack of detailed studies needed for the ADH‐II and the TCA enzyme pool, 8 of the 48 parameters were adjustable. Simulation results are presented for verification of the model which successfully described the observed phenomena for the fermentations ofS. cerevisiaestrain AB103. 1 pYαEF‐25. Also presented is a statistical analysis of the model's fit and model parameter sensiti

ISSN:0006-3592    

DOI:10.1002/bit.260350405

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe model analysis of a bioreactor with two intercalated‐spiral sets of hollow fibers with alternated dead ends is presented. Design equations are derived based on a model with two jumped fibers and an approximation of the fluid mechanics with a small fiber radius‐to‐length ratio. The performance of the bioreactor is simulated with and without cell growth utilizing a segregated radial flow model in the extracapillary space. The pressure modulus, the wall Peclet number, the Thiele modulus, and the Monod constant are used as model parameters. The results can be used to assess the proper choice of fiber permeability, fiber length, fiber spacing, and flow vel

ISSN:0006-3592    

DOI:10.1002/bit.260350406

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

年代:1990

数据来源: WILEY

摘要:

AbstractThereg 1mutation will allow the expression of a cloned gene on a plasmid under the control of aGALpromoter in the presence of glucose. The metabolism of wild‐type andreg lmutant strains was examined by in vivo31P nuclear magnetic resonance (NMR) spectroscopy. Transient profiles of glucose 6‐phosphate, fructose 6‐phosphate, fructose 1, 6‐diphosphate, and 3‐phosphoglycerate indicated that glucose was processed differently for thereg 1strain despite similar cytoplasrnic pH values and ATP levels. Intracellular phosphate became depleted in the transition to quasi‐steady state and limited glycolysis in thereg 1strain. The glucose uptake step or hexokinase step appears to be altered in thereg 1strain. Thereg 1strain utilized galactose faster than the wild‐type strain under the conditions used for NMR analysis. These results are consistent with the hypothesis that theREG 1product operates early in the regulatory circuitry for glucose repression. This study illustrates the usefulness of transient information provided by NMR in understanding changes in the metabolism of genetically manipula

ISSN:0006-3592    

DOI:10.1002/bit.260350407

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe partitioning of vancomycin in polyethylene glycol (PEG)‐dextran and PEG‐phosphate aqueous two‐phase systems was studied at different pHs, at varying concentrations of neutral salts, and with an affinity ligand attached to methoxy polyethylene glycol (MPEG). Vancomycin is found to partition preferentially into the PEG‐rich top phase, and its partition coefficient increases nearly exponentially with the addition of water structure‐making salts, such as sodium sulfate and sodium chloride, but is independent of sodium phosphate concentration. In the PEG‐dextran system the vancomycin partition coefficient increases 3‐fold in acidic and neutral solutions, while in the PEG‐phosphate system it increases about 30‐fold on the addition of the same amount of sodium chloride (1. 5 mol/kg). In basic solution, above its isoelectric point, the vancomycin partition coefficient increases slightly with NaCI concentration in the PEG‐dextran system. We also examined the use of the dipeptideD‐ala‐D‐ala as an affinity ligand on MPEG to extract vancomycin into the PEG‐rich phase. The vancomycin partition coefficient increased almost 7‐fold upon adding the MPEG‐ligand in an amount equal to approximately 3% of the total PEG in the system. Finally, fractionation of the polydisperse phase‐forming polymers in the two‐phase PEG‐dextran system was observed. The effect of this polymer fractionation on the partition c

ISSN:0006-3592    

DOI:10.1002/bit.260350408

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

年代:1990

数据来源: WILEY

摘要:

AbstractA new on‐line optimization and control procedure applicable to biotechnological systems for which a precise mathematical model is unavailable has been developed and tested. The proposed approach is based on an online search for optimum operating conditions by an automatic system using a modified simplex algorithm to which several features have been added to permit real time operation. The simplex algorithm is the upper level of a hierarchical software package in which the other levels are cost evaluation, control, data acquisition, and signal processing. The optimization method was tested in a laboratory minipond for the cultivation ofSpirulina platensis. The controlled parameters were light intensity, optical density, pH, and temperature. The proposed optimization method can be applied to other biological processes provided that the pertinent variables can be measured and controlled and the cost function can be defined mathematicall

ISSN:0006-3592    

DOI:10.1002/bit.260350409

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

年代:1990

数据来源: WILEY

摘要:

AbstractLimitations of oxygen transfer in fermentation can be solved using auxiliary liquids immiscible in the aqueous phase. The liquids (called oxygen‐vectors) used in this study were hydrocarbon (n‐dodecane) and perfluorocarbon (forane F66E) in which oxygen is highly soluble (54.9 mg/L inn‐dodecane and 118 mg/L in forane F66E at 35°C in contact with air at atmospheric pressure). It has been demonstrated that the use ofn‐dodecane emulsion in a culture ofAerobacter aerogenesenabled a 3. 5‐fold increase of the volumetric oxygen transfer coefficient(kLa) calculated on a per‐liter aqueous phase basis. The droplet size of the vector played a crucial role in the phenomena. When a static contact between gas bubble and vector droplet was established in water, the vector covered the bubble, in agreement with positive values of the spreading coefficient for these fluids. The determination of the oxygen transfer coefficients (kL) in a reactor with a definite interfacial area enabled the main resistance to be located in the boundary layer of the waterside either for a gas‐water or a vector‐water interface. Because oxygen consumption by weakly hydrophobic cells can only occur in the aqueous phase, the oxygen transfer is achieved according to the following pathway: gas‐vector‐water‐cell. Finally, a mechanism for oxygen transfer within this four‐p

ISSN:0006-3592    

DOI:10.1002/bit.260350410

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

年代:1990

数据来源: WILEY

ISSN:0006-3592    

DOI:10.1002/bit.260350401

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

年代:1990

数据来源: WILEY