摘要:

AbstractTwo methods are described for the preparation of enantiomerically pure (+)‐trans‐isochorismic acid, an important metabolite of the postchorismate pathway. Both methods can be employed to prepare isotopically labeled isochorismic acid. One of the two methods is suitable to prepare bulk quantities of isochorismic acid using a recombinant strain ofKlebsiella pneumoniae62‐1. © 1995 John Wiley&Son

ISSN:0006-3592    

DOI:10.1002/bit.260450402

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

年代:1995

数据来源: WILEY

摘要:

AbstractIntracellular fluxes are important in defining cellular physiology and its changes in response to environmental variations. Stoichiometric balances combined with extra cellular metabolite measurements were applied to the estimation of intracellular fluxes and the study of energy metabolism in the hybridoma cell line ATCC CRL 1606. Redundant measurements allowed the evaluation of the consistency of the stoichiometry, measurements, and pseudo‐steady‐state assumption leading to refinement of the assumed biochemistry and identification of measurement errors. To validate the flux estimates, two batch experiments were performed with glucose labeled in the 1 position with13C. The distribution of13C in secreted lactate was measured via nuclear magnetic resonance spectroscopy (NMR) and compared to that predicted from the estimated intracellular fluxes. There was good agreement between the measured and estimated isotope distributions, demonstrating the validity of the flux estimates obtained from stoichiometric balances. © 1995 John Wiley&Sons,

ISSN:0006-3592    

DOI:10.1002/bit.260450403

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

年代:1995

数据来源: WILEY

摘要:

AbstractRemoval of phenols and aromatic amines from industrial wastewater by tyrosinase was investigated. A color change from colorless to darkbrown was observed, but no precipitate was formed. Colored products were found to be easily removed by a combination treatment with tyrosinase and a cationic polymer coagulant containing amino group, such as hexamethylenediamine‐epichlorohidrin polycondensate, polyethleneimine, or chitosan. The first two coagulants, synthetic polymers, were more effective than chitosan, a polymer produced in crustacean shells. Phenols and aromatic amines are not precipitated by any kind of coagulants, but their enzymatic reaction products are easily precipitated by a cationic polymer coagulant. These results indicate that the combination of tyrosinase and a cationic polymer coagulant is effective in removing carcinogenic phenols and aromatic amines from an aqueous solution. Immobilization of tyrosinase on magnetite gave a good retention of activity (80%) and storage stability i.e., only 5% loss after 15 days of storage at ambient temperature. In the treatment of immobilized tyrosinase, colored enzymatic reaction products were removed by less coagulant compared with soluble tyrosinase. © 1995 John Wiley&Sons, I

ISSN:0006-3592    

DOI:10.1002/bit.260450404

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

年代:1995

数据来源: WILEY

摘要:

AbstractMethods for the selection of transfectoma cells that express large quantities of mouse–human chimeric antibodies have been develped. SP2/0 mouse myeloma cells were transfected with pSV2‐gptand pSV2‐neobased immunoglobulin expression vectors. Double transfectants were selected using the xanthine–guanine phosphoribosyl transferase (gpt)and the neomycin (neo) selection marker genes. ELISA‐based screening of transfectoma clones resulted in the isolation of IgG‐producing transfectomas. Introduction of the kappa light‐chain 3′‐enhancer into the light‐chain expression vector significantly increased immunoglobulin expression, but only when the enhancer was located at its physiological site, 9 kb downstream of the kappa constant region exon. With some of the transfectomas, final yields of up to 80 mg/L of chimeric IgG were obtained in conventional flask cultures using serum‐free growth medium. A pilot‐scale AcuSyst Maximizer hollow fiber cell culture system was used for the production of gram amounts of chimeric IgG. Results obtained with different transfectoma clones in conventional culture were not fully predictive for yields in the hollow fiber system. In contrast, differences in productivity between individual clones in the laboratory‐scale Tecnomouse cell culture unit were comparable with those in the Maximizer system. Up to 200 mg of chimeric IgG were produced per day in one Maximizer bioreactor. ©

ISSN:0006-3592    

DOI:10.1002/bit.260450405

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

年代:1995

数据来源: WILEY

摘要:

AbstractLactic acid production with cell recycling on an ultrafiltration tubular membrane reactor was studied; higher lactic acid concentrations as well as productivities were obtained under long‐term fermentations compared with other high cell density systems. Different operational conditions, namely dilution rates and start‐up modes, were assessed. Performances were very different at the three different dilution rates tested (D= 0.20 h−1,D= 0.40 h−1, orD= 0.58 h−1). The different behaviours are discussed and factors responsible for them are presented. The best way to operate for lactic acid production is chosen, the dilution rate ofD= 0.40 h−1being the one providing the best overall performance. On the other hand, results show that of the two start‐up modes tested, continuous start (membrane open) permits higher permeabilities throughout the operational runs than batch start (membrane closed). Operational stability was found to be directly associated with membranes that work at “steady state,” the membrane permeability being kept around 15 L/m2h. Optimized cell bleed can improve time of operation if such membrane permeability can be maintained for a longer time. A comparison of results with those obtained in other lactic acid production systems is presented; such comparison shows that this tubular ultrafiltration membrane cell recycle reactor presents three important advantages: (1) concomitant lactic acid concentrations and productivities; (2) long periods of operation at reasonable permeabilities; and (3) good mechanical stability permitting the use of steam sterilization. © 1995 Jo

ISSN:0006-3592    

DOI:10.1002/bit.260450406

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

年代:1995

数据来源: WILEY

摘要:

AbstractRecycling of cellulases should lower the overall cost of lignocellulosiic bioconversion processes. In this study, three recycling strategies were evaluated to determine their efficiencies over five successive rounds of hydrolysis. The effect of lignin on recycling was examined by comparing water‐washed, steam‐exploded birch (WB; 32% lignin) and WB which had been further extracted with alkali and peroxide (PB; 4% lignin). When the cellulases were recovered from the residual substrates after partial hydrolysis of both substrates, the recovered cellulase activity toward the mixture of fresh and residual substrates decreased after each recycling step. When the cellulases in the supernatants were also recycled, up to 20% more activity could be recovered. In both of these cases, the recovered activities did not correspond to the activities expected from the amount of cellulase protein recovered during recycling. The best recovery was obtained when the cellulases were recovered from both the residue and the supernatant after complete hydrolysis of the PB substrate. In this case, all of the originally added cellulase activity could be recovered for four consecutive hydrolysis rounds. However, when the same recycling strategy was carried out using the WB substrate, the recovered cellulase activity declined quickly with each recycling round. In all three of the recycling strategies, lower cellulase activities were recovered from the substrates with higher lignin contents. © 1995 John Wiley&Sons,

ISSN:0006-3592    

DOI:10.1002/bit.260450407

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

年代:1995

数据来源: WILEY

摘要:

AbstractDielectrophoresis is the movement of particles in non‐uniform alternating and direct current (AC, DC) electric fields. When nonuniform electric fields are created between microelectrodes, cells will redistribute themselves around the electrodes, the force holding the cells in place dependig on the local electric field and on the electrical properties of the cells themselves and the suspending medium. Steric drag forces produced by a gentle fluid flow in the chamber can be used to separate cells by selectively lifting cells from potential energy wells produced by the electric field. The technique is demonstrated in the batch separation of bacteria, yeast cells, and plant cells. Continuous separation and extraction of two cell types can be achieved by repeated reversing of the fluid flow direction in phase with the switching on and off of the applied voltage, and the efficacy of the technique is demonstrated for viable and nonviable (heat‐treated) yeast cells. © 1995 John Wiley&Sons,

ISSN:0006-3592    

DOI:10.1002/bit.260450408

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

年代:1995

数据来源: WILEY

摘要:

AbstractChromobacterium viscosum(CV) lipase solubilized in water‐in‐oil (w/o) microemulsions based on the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) have been used for multigram‐scale ester synthesis, including the kinetic resolution of a secondary alcohol. The stability of CV lipase in all the CTAB microemulsions studied was excellent and was superior to that observed in aqueous buffer at the same pH and temperature. Kinetic studies were performed using the synthesis of ethylhexadecanoate as a model reaction. Under pseudo‐first‐order conditions, the synthesis rates were linearlydependent on the enzyme and fatty acid concentrations and theRdependence shows the characteristic bell‐shaped curve (whereR= [H2O]/[surfactant]). The dependence of enzyme activity toward octyldecanoate synthesis on the pH of the dispersed buffer phase is in marked contrast to that observed for the pH dependence of CV lipase towardp‐nitrophenylbutyrate hydrolysis. In the former case, the pH‐activity profile is approximately sigmoidal, which may reflect the ionization state of the fatty acid substrate. In the latter case, the pH dependence is minimal at bothR= 10 andR= 50, suggesting the enzyme does not experience a changed pH environment. Inclusion of a pH‐sensitive probe molecule into those incubations containing fatty acid clearly demonstrates that the probe molecule experiences a changed environment consistent with that expected for the selected buffer. An in situ Fourier transform nuclear magnetic resonance (FT‐NMR) assay has been developed which allows continuous monitoring of the esterification reactions, thereby providing an additional means of determining initial rates. The method may be of general value for lipase assays in microemulsions since it may provide, at the same time, information regarding enzyme regioselectivity. © 1995

ISSN:0006-3592    

DOI:10.1002/bit.260450409

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe fermentation kinetics for separate as well as simultaneous glucose and xylose fermentation with recombinant ethanologenicEscherichia coliKO11 are presented. Glucose and xylose were consumed simultaneously and exhibited mutual inhibition. The glucose exhibited 15 times stronger inhibition in xyclose fermentation than vice versa. The fermentation of condensate from steampretreated willow (Salix) was investigated. The kinetics were studied in detoxified as well as in nondetoxified condensate. The fermentation of the condensate followed two phases: First the glucose and some of the pentoses (xylose in addition to small amounts of arabinose) were fermented simultaneously, and then the remaining part of the pentoses were fermented. The rate of the first phase was independent of the detoxification method used, whereas the rate of the second phase was found to be strongly dependent. When the condensate was detoxified with overliming in combination with sulfite, which was the best detoxification method investigated, the sugars in the condensate, 9 g/L, were fermented in 11 h. The same fermentation took 150 h in nondetoxified condensate. The experimental data were used to develop an empirical model, describing the batch fermentation of recombinantE. coliKO11 in the condensate. The model is based on Monod kinetics including substrate and product inhibition and the sum of the inhibition exerted by the rest of the inhibitors, lumped together. © 1995 John Wiley&Sons, Inc

ISSN:0006-3592    

DOI:10.1002/bit.260450410

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

年代:1995

数据来源: WILEY

摘要:

AbstractCellulase was modified with amphilic copolymers made of α‐allyl‐ω‐methoxy polyoxyalkylene (POA) and maleic acid anhydride (MAA) to improve the cellulose hydrolytic reactivity and cellulase separation. Amino groups of the cellulase molecule are covalently coupled with the MAA functional groups of the copolymer. At the maximum degree of modification (DM) of 55%, the modified cellulase activity retained more than 80% of the unmodified native cellulase activity. The modified cellulase shows greater stability against temperature, pH, and organic solvents, and demonstrated greater conversion of substrate than native cellulase does. Cellulase modification is also useful for controlling strong adsorption of cellulase onto substrate. Moreover, cellulase modified with the amphiphilic copolymer displays different separation characteristics which are new. One is a reactive two‐phase partition and another is solubility in organic solvents. It appears that these characteristics of modified cellulase work very effectively in the hydrolysis of cellulose as a total system, which constitutes the purification of cellulase from culture broth, hydrolysis of cellulose, and recovery of cellulase from the reaction mixture. © 1995 John Wiley

ISSN:0006-3592    

DOI:10.1002/bit.260450411

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

年代:1995

数据来源: WILEY