摘要:

AbstractSpray columns can be used to isolate and purify proteins using the two‐phase aqueous extraction technique based on polyethylene glycol (PEG) and dextran. The fractional dispersed phase (PEG) holdup and overall mass transfer coefficients were measured in a 9.7 mm i.d. spray column. We found that the dispersed phase holdup increased with increasing PEG phase velocity. The overall mass transfer coefficients for bovine serum albumin, normalized for the PEG holdup, were found to be independent of the PEG phase velocity. This result was expected, since true mass transfer coefficients do not vary with phase velocit

ISSN:0006-3592    

DOI:10.1002/bit.260360202

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

年代:1990

数据来源: WILEY

摘要:

AbstractA supported liquid membrane system was developed for the extraction of ethanol during semicontinuous fermentation ofSaccharomyces bayanus.it consisted of a porous Teflon sheet as support, soaked with isotridecanol. This assembly permitted combining biocompatibility, permeation efficiency, and stability. The removal of ethanol from the cultures led to decreased inhibition and, thus, to a gain in conversion of 452 g/L glucose versus 293 g/L glucose without extraction. At the same time, the ethanol volumetric productivity was enhanced 2.5 times, due to an improvement of yeast viability, while the substrate conversion yield was maintained above 95% of its theoretical value. Besides these improvements in fermentation performances, the process resulted in ethanol purification, since the separation was selective towards microbial cells and carbon substrate, and likely selective to mineral ions present in the fermentation broth. For pervaporation, a concentration of ethanol four times greater was obtained in the collected permeate.

ISSN:0006-3592    

DOI:10.1002/bit.260360203

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

年代:1990

数据来源: WILEY

摘要:

AbstractRecombinant cell growth and protein synthesis by a recombinantEscherichia coliunder various inducing conditions are compared to the predictions of a mathematical model. The mathematical model used was a combination of two literature models: (1) an empirical kinetic model for recombinant growth and product formation and (2) a genetically structured model of thelacpromoter‐operator on a multicopy plasmid. The experimental system utilized was recombinantE. coliCSH22 bearing the temperature‐sensitive plasmid pVH106/172, which codes for the synthesis of β‐galactosidase and the otherlacoperon genes under the control of alacpromoter. Mathematical model predictions for recombinant β‐galactosidase yield and specific growth rate were compared with fermentation measurements of these same quantities for conditions of chemical induction with cyclic AMP and IPTG, copy number amplification (by shifting culture temperature), and combined chemical induction and copy number amplification. The model successfully predicted experimental product yields for most cases of chemical induction even though the product yields varied from 0.34 × 103to 1500 × 103units/g cell mass. The kinetic model also correctly predicted a decline in the specific growth rate with increasing levels of plasmid and recombinant protein. The model was less successful at predicting product amplification at high copy numbers. A comparison of model predictions and experimental results was also used to investigate some of the assumptions used in constructing the mathemat

ISSN:0006-3592    

DOI:10.1002/bit.260360204

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

年代:1990

数据来源: WILEY

摘要:

AbstractA technique for enzyme reuse and product recovery from enzymatic catalysis in microemulsions is demonstrated. The enzymatic reaction is performed in a homogeneous isotropic microemulsion; AOT (sodium bis‐(2‐ethyl‐ hexyl)sulfosuccinate)/isooctane/buffer or C12E5(penta ethylene glycol dodecyl ether)/heptane/buffer. By small temperature changes the systems are shifted to two phase regions, where an oil‐rich phase, containing the product, coexists with a water‐rich phase containing surfactant and enzyme. The oil‐rich phase may be replaced by an oil solution containing new substrate. Thus, the reaction may be continued and the enzyme reused. This procedure was repeated nine times in the present study. Data on phase behavior in presence and in absence of protein, partitioning of the components and a radioactive‐labelled protein between the phases, and the repeated use of horse liver alcohol dehydrogenase (HLADH) in the microemulsions

ISSN:0006-3592    

DOI:10.1002/bit.260360205

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

年代:1990

数据来源: WILEY

摘要:

AbstractA bioenergetic model has been developed for the fermentation of glucose byBacillus polymyxa. This model uses energy balances to determine which pathways are utilized by the substrate. The model can predict substrate consumption, biomass formation, and the product distribution for this fermentation. The products are carbon dioxide, water, 2,3‐butanediol, and ethanol, where ethanol represents lumped anaerobic product

ISSN:0006-3592    

DOI:10.1002/bit.260360206

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe concept of a charged membrane bioreactor (CMBR) has been proposed for continuous reactions of enzymatic reduction dependent upon the nicotinamide coenzyme NADP(H). It was found that a composite membrane with a negative charge, NTR 7410, could retain NADP(H) selectively without any chemical modification. Several permeation experiments have revealed that the retainment of a coenzyme is based on electrostatic repulsion of negative charges between the membrane and the phosphate moiety of NADP(H). The retainment ratio was reduced by the addition of inorganic salt, although it could be restored to 0.8 in the presence of albumin. A reactor equipped with a charged membrane as the coenzyme separator module was constructed and used in the continuous production of sorbitol. NADPH‐dependent aldose reductase isolated fromCandida tropicalisIAM 12202 was used for the production of sorbitol from glucose. The coenzyme oxidized in this reaction was enzymatically regenerated by conjugation with glucose dehydrogenase, together with the coproduction of gluconic acid from glucose. With a substrate conversion of 85%, 100 g/L sorbitol was produced and equimolar gluconic acid was coproduced for more than 800 h, indicating that the reaction was efficiently coupled to the enzymatic regeneration. The initial high retainment ratio of the membrane was almost maintained throughout the entire reaction. Consequently, the turnover number of the coenzyme reached 106,00

ISSN:0006-3592    

DOI:10.1002/bit.260360207

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

年代:1990

数据来源: WILEY

摘要:

AbstractA theoretical model was constructed in order to study charged membrane bioreactors (CMBRs). In this model, it was postulated that a native nicotinamide coenzyme NADP(H) can be partially retained by a charged membrane in continuous operation. A multienzyme system composed of NADPH‐dependent aldose reductase (AR) and glucose dehydrogenase (GDH) was used for the production of sorbitol and gluconic acid from glucose and for the conjugated enzymatic regeneration of NADP(H). Both enzymes were studied with respect to their reaction kinetics. AR was determined to obey the Theorell–Chance mechanism. GDH reaction was approximated by the initial velocity equation of the sequential Bi–Bi mechanism since the reverse reaction could be neglected. Significant inhibitions of both enzymes by sorbitol, gluconic acid, and glucose were observed, and the mode of inhibition was estimated to modify the velocity equations. The differential equation system for each component was derived and numerically analyzed according to the model. The theoretical model elucidated several features of the CMBR. (1) When compared at the same productivity, higher retainment was found to bring about a higher coenzyme turnover number, indicating that the feed coenzyme concentration can be reduced. (2) Under constant conversion, a contradictory relationship between turnover number and residence time arises if the feed concentration of a coenzyme varies. The theoretical model predicts that there is a practically optimal concentration for using NADP(H) efficiently. This concentration was consistent with that yielding the estimated minimum total cost. (3) In this system, excess‐GDH‐to‐AR activity was required because of differences in their kinetic constants. The amount of regeneration enzyme required can be reduced by the accumulation of excels NADPH due to coenzyme retainment. (4) Comparison with an ideal repeated batch reaction revealed that the continuously operated CMBR was vastly superior with respect to productivity as well as operat

ISSN:0006-3592    

DOI:10.1002/bit.260360208

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe notion that the regulated and flux‐controlling enzyme in a metabolic network need not correspond suggests that the purpose of regulation may not be flux homeostasis under all physiological circumstances. Additionally, the fact that diversity in the function of intact metabolic networks exists suggests that in addition to time constant separation, other kinetic structure/regulatory mechanism patterns exist. In order to compliment and expand prior work on identifying kinetic structure–property relationships in networks, the present work explores in a general way how the control, dynamic, and energetic properties of metabolic networks depend on operating point, kinetic structure, and regulatory mechanism. The basic feature of trade‐offs between properties is illustrated and used as a basis for indicating how particular subsets of structure, regulatory mechanism, and operating point emphasize certain properties that can be associated with a physiological function. Examples of scavenging trace metabolites and amphibolite coordination are proposed. Microstructure logic in terms of turnover number distributions as well as a potential mixed polynomial network analysis approach are also disc

ISSN:0006-3592    

DOI:10.1002/bit.260360209

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe representation of metabolic network reaction kinetics in a scaled, polynomial form can allow for the prediction of multiple steady states. The polynomial formalism is used to study chemostat‐culturedEscherichia coliwhich has been observed to exhibit two multiple steady states under ammonium ion‐limited growth conditions: a high cell density–low ammonium ion concentration steady state and a low cell density–high ammonium ion concentration steady state. Additionally, the low‐cell‐density steady state has been observed to drift to the high‐cell‐density steady state. Inspection of the steady‐state rate expressions for the ammonium ion transport/assimilation network (in polynomial form) suggests that at low ammonium ion concentrations, two steady states are possible. One corresponds to heavy use of the glutamine synthetase‐glutamate synthase (GLNS–GS) branch and the second to heavy use of the glutamate dehydrogenase (GDH) branch. Realization of the predicted intracellular steady states is also found to be dependent on the parameters of the transport process. Moreover, the two steady states differ in where their energy intensity lies. To explain the drift, GLNS, which is inducible under low ammonium ion concentrations, is suggested to be a “memory element.” A chemostat‐based model is developed to illustrate that perturbations in dilution rate can lead to drift between the two steady states provided that the disturbance in dilution rate is sufficiently la

ISSN:0006-3592    

DOI:10.1002/bit.260360210

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

年代:1990

数据来源: WILEY

摘要:

AbstractMeasurements of volume distributions and dry weight are made on hybridoma cells in culture. The volume of viable hybridoma cells is significantly larger than that of nonviable cells. During exponential growth, the volume of the viable hybridoma cells is found to be significantly larger than that during other stages of batch culture. Proportionality is found between the volume of the cells and their dry weight, indicating that the volume data can be used in conjunction with cell concentration data as a practical technique for indirect measurement of the biomass concentration present in a culture. Comparison of dry weight concentrations in continuous culture to predictions from the volume data shows very good agreement.

ISSN:0006-3592    

DOI:10.1002/bit.260360211

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

年代:1990

数据来源: WILEY