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Evaluation of Alcaligenes eutrophus cells as an NADH regenerating catalyst in organic-aqueous two-phase system
A soluble NAD-dependent hydrogenase contained in Alcaligenes eutrophus was evaluated as a coenzyme regenerating catalyst in an organic-aqueous two- phase (predominantly organic) system. The horse-liver alcohol-dehydrogenase (HLADH) catalyzed reduction of cyclohexanone to cyclohexanol was used as a model reaction. The impact of different solvents (selected to span a large variety of principal prope
Coenzyme-dependent oxidoreductions in organic media
Intrinsic α-chymotrypsin activity determination in acetonitrile containing small amounts of aqueous buffer
Sidedness of plant plasma membrane vesicles purified by partitioning in aqueous two-phase systems
Triacylglycerols of Vernonia galamensis seed oil
Separation methods using silica gel column chromatography and preparative thin layer chromatography were employed to prepare pure triacylglycerol fractions of the oil from Vernonia galamensis seeds. Pure vernolic acid (12, 13-epoxy-octadec-cis-9-enoic acid) was prepared by enzymatic hydrolysis of the chromatographically purified major triacylglycerol, trivernolin, using a commercially available im
Physical characterization of porous materials and correlation with the activity of immobilized enzyme in organic medium
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
Water activity control in enzymatic esterification processes
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
Water transfer kinetics in a water activity control system designed for biocatalysis in organic media
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 enantiomeric purity of alcohols formed by enzymatic reduction of ketones can be improved by optimisation of the temperature and by using a high co-substrate concentration
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
Preparation of diglycerides by lipase-catalyzed alcoholysis of triglgicerides
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
Enantioselectivity of lipases : Effects of water activity
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
How do additives affect enzyme activity and stability in nonaqueous media?
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 hydrogenase, a coenzyme regenerating catalyst for NADH-dependent oxidoreductases
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
Structural characterization of two aquaporins isolated from native spinach leaf plasma membranes
Oxidative cross-linking of plasma membrane arabinogalactan proteins
An abundant TIP expressed in mature highly vacuolated cells
Lipid composition of plasma membranes from barley leaves and roots, spinach leaves and cauliflower inflorescences
Characterization and optimization of phospholipase A2 catalyzed synthesis of phosphatidylcholine
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
Evaluation of electron mediators for the electromicrobial reduction of chloropyruvate by Proteus vulgaris cells
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