A series of commonly used porous supports was characterized by determination of particle size distribution, porosity, surface area (total and distributions with pore diameters) and skeletal density. The performance of immobilized α-chymotrypsin catalyzed dipeptide synthesis in an acetonitrile medium was correlated with these physical properties.At high enzyme loading, when internal mass transfer l

Lipase-catalyzed (Lipozyme IM 20 and Novozyme SP 435) esterification reactions in 5-methyl-2-hexanone were studied in order to investigate the practical application of a water activity control system consisting of a semipermeable silicone tubing and saturated salt solutions. The system used successfully in different reactor configurations [butch, continuous stirred-tank reactor (CSTR), and tubular

The performance of a water activity-controlling system in organic solvents using saturated salt solutions circulating in silicone tubing submerged in the solvent was studied. The mass transfer could be regarded as a flux through a cylindrical geometry. Integration over the barrier gave diffusion coefficients of water (D(aw)) which were similar for the different tubing sizes used. The driving force

The stereoselective reduction of ketones by alcohol dehydrogenase from Thermoanaerobium brockii was studied in organic reaction media, 2-Propanol was used as co-substrate to regenerate the coenzyme NADPH. The enantiomeric excess of the alcohol formed from the ketone decreased during the course of the reaction (from 53 to 0% e.e. in the formation of (R)-2-butanol). This was interpreted as being due

Lipase from Penicillium roquefortii immobilized on porous polypropylene particles was used for enzymatic preparation of 1,2-diglycerides by alcoholysis in organic media. A screening of commercially available lipases showed that lipases from Penicillium species produced high amounts of 1,2-diglycerides from triglycelirles. Reaction parameters such as solvent, alcohol, water activity, and fatty acid

The enantioselectivity (E) of lipases in esterifications of secondary alcohols with decanoic acid was studied in organic media. The enantioselectivity of 2-octanol differed greatly among the lipases used. Candida antarctica lipase was extremely selective (E= 9 000) while Candida rugosa lipase was much less selective (E= 1.7). Other enzymes (Lipozyme and lipases from Pseudomonas and Rhizopus arrhiz

The catalytic activities of lyophilized powders of α-chymotrypsin and Candida antarctica lipase were found to increase 4- to 8-fold with increasing amounts of either buffer salts or potassium chloride in the enzyme preparation. Increasing amounts of sorbitol in the chymotrypsin preparation produced a modest increase in activity. The additives are basically thought to serve as immobilization matric

Alcaligenes eutrophus cells containing a soluble NAD-dependent hydrogenase was evaluated as a NADH regenerating catalyst. In the presence of hydrogen and permeabilized A. eutrophus cells, NADH regeneration was achieved, and reductions catalyzed by horse liver alcohol dehydrogenase and lactate dehydrogenase proceeded to 90-99% conversion. The operational stability of the hydrogenase was improved by

The phospholipase A2 (PLA2) catalyzed synthesis and hydrolysis of phosphatidylcholine (PC) was studied in a water activity controlled organic medium. The aim of the study was to find the conditions most favorable for the synthetic reaction. To do this, the impact of various parameters such as water activity, substrate concentration and temperature on enzyme activity and equilibrium yield was deter

Different electron mediators were evaluated for the electromicrobial reduction of chloropyruvate to chlorolactate. The reaction was catalyzed by a mediatol-dependent D-lactate dehydrogenase in whole cells of Proteus vulgaris and yielded D-(S)-chlorolactate with high optical purity (> 97% e.e.). The ideal mediatol should favor a high rate in the enzymatic reaction and a low rate in the nonenzymatic

Diol fatty acid esters find a variety of industrial applications. The use of lipases in microaqueous environment provides an attractive route for synthesis of fatty acyl esters of ethylene glycol. The effect of various process parameters that play key roles in delineating reaction kinetics and distribution of mono- and diesters in the product have been studied.

Immobilized α-chymotrypsin was used as catalyst for studying temperature effects on acyl transfer reactions (acyl-donor: Bz-TyrOEt) in a water-immiscible organic solvent. The solubility of the two nucleophiles, Phe-NH2 and water, decreased with decreasing temperature. The relative decrease for the amide was larger (2.4-fold) than for water. Therefore the thermodynamic activity (estimated by the re

An approach was developed for the isolation and characterization of soybean plasma membrane-associated proteins by immunoscreening of a cDNA expression library. An antiserum was raised against purified plasma membrane vesicles. In a differential screening of approximately 500,000 plaque-forming units with the anti-(plasma membrane) serum and DNA probes derived from highly abundant clones isolated

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