摘要:

AbstractThrough simple model analysis, the mass action kinetic model for lipolytic enzymes in biphasic aqueous‐organic systems can be simplified using the quasi–steady state assumption (or the quasi–equilibrium state assumption) for the adsorbed enzymeE* or the enzyme–substrate complexE*S. Some parameter combinations leading to the above assumptions are derived confirmed by full numerical integration of the whole enzymatic process. The results may be classified into three categories: (1) the quasi–equilibrium state assumption forE*, (2) the quasi–steady state assumption forE*, and (3) the quasi–steady state assumption forE*S. Further simplification for bothE* andE*Sis also discussed. © 1993 W

ISSN:0006-3592    

DOI:10.1002/bit.260410602

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe growth ofThiobacillus ferrooxidanson sulphur is known to proceed through the attachment of cells to the sulphur particles. Experiments, However, show that the cells in the liquid phase, which are not attached to the sulphur particles, also grow. It has been shown through the use of a two‐compartment membrane reactor that this increase is partially due to the release of ions, corresponding to partially oxidized of sulphur, into the solution by the attached cells. The main soluble ion has been found to the thiosulphate, but traces of sulphite have also been detected. © 1993 John Wiley&Sons, I

ISSN:0006-3592    

DOI:10.1002/bit.260410603

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

年代:1993

数据来源: WILEY

摘要:

AbstractFactors affecting the performance of crossflow filtration were investigated with a thin‐channel module and yeast cells. In crossflow filtration ofSaccharomyces cerevisiaecells cultivated with YPD medium (Yeast extract, polypeptone, and dextrose) and suspended in saline, a steady state was attained within several minutes when the cell concentration was low and the circulation flow rate was high. The steady‐state flux and the change in flux during the initial unsteady state were explained well by conventional filtration theory, with the amount of cake deposited and the mean specific resistance to the cake measured in a dead‐end filtration apparatus used in calculation. When the circulation flow rate was lower than a critical value, a part of the channel of the crossflow filtration module was plugged with cell cake, and thus the steady‐state flux was low. In crossflow filtration of suspensions of commercially available baker's yeast, the flux gradually decreased, and the flux after 8 h of filtration was lower than the value calculated by filtration theory. Fine particles contaminating the baker's yeast was responsible for the decrease. A similar phenomenon was responsible for the decrease. A similar phenomenon was observed in crossflow filtration of a broth ofS. cerevisiaecells cultivated in molasses medium, which also contains such particles, had no effect of the permeation flux during crossflow filtration. © 1993 John Wiley&S

ISSN:0006-3592    

DOI:10.1002/bit.260410604

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

年代:1993

数据来源: WILEY

摘要:

AbstractTo determine when intraparticle diffusion and sorption can influence the rate of biodegradation, we consider the biodegradation of a pollutant diffusing into or out of porous aggregates suspended in a liquid medium, where the reactant is metabolized by bacteria. The pollutant that diffuses into the aggregates obeys a sorption–desorption equilibrium isotherm at sites on inner pore surfaces. The governing partial differential equations for the transient process describe (a) the local equilibrium sorption–desorption and the diffusion of the pollutant in the porous aggregate, (b) the mass transfer of the pollutant from the external surface of the spherical aggregates to the reaction medium, and (c) the biodegradation of the pollutant in the external medium. Illustrative calculations are presented for a linear sorption calculations are presented for a linear sorption isotherm and first‐order biodegradation kinetics. A dimensionless group, comprised of the diffusion coefficient, biodegradation rate coefficient, aggregate characteristics length (radius), and adsorption capacity, serves as a criterion for determining when intraparticle diffusion can be ignored. The model provides a realistic description of experimental data for biodegradation of a pollutant subject to intraparticle diffusion and sorption. © 1993 John Wiley&Son

ISSN:0006-3592    

DOI:10.1002/bit.260410605

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe two main contributions of this are the solidification ofCorynebacterium glutamicumbiochemistry guided by bioreaction network analysis, and the determination of bansal metabolic flux distributions during growth and lysine synthesis. Employed methodology makes use of stoichiometrically based mass balances to determine flux distributions in theC. glutamicummetabolic network. Presented are a brief description of the methodology, a through literature review of glutamic acid bacteria biochemistry, and specific results obtained through a combination of fermentation studies and analysis‐directed intracellular assays. The latter include the findings of the lack of activity of glyoxylate shunt, and that phosphoenolpyruvate carboxylase (PPC) is the only anaplerotic reaction expressed inC. glutamicumcultivated on glucose minimal media. Network simplifications afforded by the above findings facilitated the determination of metabolic flux distributions under a variety of culture conditions and led to the following conclusions. Both the pentose phosphate pathway and PPC support fluxes during growth and lysine overproduction branch point does not appear to limit lysine synthesis. © 1993 John Wiley&Sons, I

ISSN:0006-3592    

DOI:10.1002/bit.260410606

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

年代:1993

数据来源: WILEY

摘要:

AbstractPhosphorus‐31 nuclear magnetic resonance (31P NMR) was used to compare the anaerobic metabolism of glucose by suspended and gel‐entrappedSaccharomyces bayanuscells. The fermentation of glucose was carried out in a reaction system with continuous circulation through the NMR sample tube. The intracellular pH and the levels of some phosphorylated compounds were the levels of some phosphorylated compounds were noninvasively monitored by31P NMR while glucose, fermentation products, and biomass were determined by analytic techniques comparisons showed that no significant differences are observed in the relative concentrations in the spectra, but distinct profiles for the variation of both intracellular and extracellular pH are found. The internal pH of immobilized cells is maintained at a constant value throughout the fermentation as opposed to freely suspended cells for which a steady decrease in the internal pH occurs. A faster and stronger acidification is also observed in the external medium of the assays with suspended cells. Furthermore, higher yields for ethanol and biomass production and lower yields of fermentation by‐products are obtained with immobilized cells. It is concluded that the higher intracellular pH achieved in the presence of the gel matrix had a regulatory effect on the metabolism which favored the ethanol production pathway. © 1993 John Wiley&Son

ISSN:0006-3592    

DOI:10.1002/bit.260410607

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

年代:1993

数据来源: WILEY

摘要:

AbstractIn an enzymatic synthesis of cephalexin (CEX) using an acylase fromXanthomonas citri, the effect of polyethylene glycol (PEG) on the synthetic reaction of 7‐amino‐3‐deacetoxycephalosporanic acid (7‐ADCA) andD‐alpha‐phenyl‐glycine methyl ester (PGM) to CEX was investigated. The addition of PEG (MW 300–20,000) increased the yield significantly. This yield enhancement effect tended to increase with the increasing molecular weight of PEG. Addition of PEG to the reaction system did not affect both the CEX and PGM hydrolytic reactions. The PEG added to the reaction medium used in these experiments did not depress the water activity significantly, and the product yield improvement could not be explained by the activity alone. The PEG stabilized the enzyme activity to some extent, but this stabilizing effect was only partially attributable to the yield enhancement of CEX. The enhancing effect of PEG on the synthetic yield increased with the increasing PEG molecular weight or the length of the poly(oxy‐1,2‐ethanediyl) chain, which increases the hydrophobicity of PEG. This finding consequently has led to the conclusion that the PEG structure renders the affinity between enzyme and 7‐ADCA, which is a hydrophobic substrate. The microenvironmental hydrophobicity of PEG and its interaction with the hydrophobic substrate was found to be the main reason for the improvement of the CEX yield. In fact, the Michaelis–Menten kinetic constant for 7‐ADCA,K7‐ADCAin the presence of PEG was smaller than that in the control system (without PEG addition).

ISSN:0006-3592    

DOI:10.1002/bit.260410608

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

年代:1993

数据来源: WILEY

摘要:

AbstractTogether with flow injection analysis (FIA), a chemiluminescence (CL) fiber optic biosensor system has been developed for determining glutamine in animal cell cultures. Glutaminase (GAH) and glutamate oxidase (GLO) were onto separate porous aminopropyl glass beads via glutaraldehyde activation and packed to form an enzyme column. These two enzymes acted in sequence on glutamine to produce hydrogen peroxide, which was then reacted with luminol in the presence of ferricyanide to produce a light signal. An anion exchanger was introduced on‐line to eliminate interfering endogenous glutamate in view of its negative charge at pH above 3.22 (isoelectric pH). Among several resins tested, the acetate form was most effective, and this type of ion exchanger also effectively adsorbed uric acid, acetaminophen, and aspartic acid.There was an excellent linear relationship between the CL response and standard glutamine concentration in the range 1 to 100 μM. A complete analysis could be performed in 2 min, including sampling and washing with a good reproducibility (± 4.4%). Both the bi‐enzymic and ion exchange columns were useful for at least 500 analyses when the biosensor system was applied for the glutamine determination in murine hybridoma cell cultures and insect cell cultures. The values obtained compared well with those of HPLC, thus validating the applicability of the CL fiber optic system. © 1993 John Wiley&Son

ISSN:0006-3592    

DOI:10.1002/bit.260410609

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

年代:1993

数据来源: WILEY

摘要:

AbstractEscherichia coliDH5α, carrying the pUC19 plasmid for thelacZfragment of β‐galactosidase and ampicillin resistance, was grown in a batch fermentor under conditions of fluctuating oxygen supply. A Monte Carlo method was used to control the on/off supply of air to simulate circulation of cells in a large fermentor. Rapid changes in oxygen supply reduced the rates of oxygen uptake the carbon dioxide release and prolonged the active second growth phase in batch culture, compared to growth with continuous aeration. Amplification of the plasmid was observed during the stationary phase when air supplied continuously, but not during the Monte Carlo experiments. © 1993 John Wiley&Sons,

ISSN:0006-3592    

DOI:10.1002/bit.260410610

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

年代:1993

数据来源: WILEY

摘要:

AbstractMicrobial desulfurization might be developed as a new process for the removal of pyrite sulfur from coal sluries such as coal–water mixture (CWM). An application of iron‐oxidizing bacteriumThiobacillus ferrooxidansto flotation would shorten the periods of the microbial removal of pyrite from some weeks by leaching methods to a few minutes. The floatability of pyrite in flotation was mainly reduced byT. ferrooxidansitself rather than by other microbial substances in bacterial culture as additive of flotation liquor. Floatability was suppressed within a few seconds by bacterial contact. The suppression was proportional to increasing the number of cells observed between bacterial adhesion and the suppression of floatability. If 25% of the total pyrite surface area covered with the bacteria, pyrite floatability would be completely depressed. Bacteria that lost their iron‐oxidizing activities by sodium cyanide treatment were also able to adhere to pyrite and reduced pyrite floatability as much as normal bacteria did.Thiobacillus ferrooxidansATCC 23270, T‐1, 9, and 11, which had different iron‐oxidizing abilities, suppressed floatability to similar‐levels. The oxidizing ability of bacteria did not influence the suppressing effect. These results showed the mechanism of the suppression of pyrite floatability by bacteria. Quick bacterial adhesion to pyrite induced floatability suppression by changing the surface property from hydrophobic. The quick adhesion of the bacterium was the novel function which worked to change the surface property of pyrite to remove it from coal. © 1993 John Wil

ISSN:0006-3592    

DOI:10.1002/bit.260410611

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

年代:1993

数据来源: WILEY