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α-Chymotrypsin immobilized on celite catalyzing a kinetically controlled dipeptide synthesis reaction in acetonitrile medium showed an odd behavior in response to additions of triethylamine to the reaction mixture. This base is used to deprotonate the nucleophilic reagent, l-alaninamide hydrochloride, in order to increase its nucleophilicity and solubility. However, the enzyme performance is appar
The influence of different reaction systems on α-chymotrypsin-catalyzed synthesis of eledoisin and LH-RH peptides from (7+4) and (5+5) fragments was investigated. The peptide yield was determined in the following systems: buffered aqueous media, frozen solutions, organic media, and cosolvent mixtures. The experimental set up was tailored to allow the screening of an array of conditions with minimu
The stereoselective reduction of 2-pentanone by alcohol dehydrogenase from Thermoanaerobium brockii was studied at controlled water activity and at different reaction temperatures. The reaction rate increased when water activity was increased from 0.32 to 0.96 and when raising the temperature from 5°C to 40°C. The enantioselectivity, E, reached a plateau value at high water activities. The enantio
Hydroxy carboxylate viologen oxidoreductase (HVOR) contained in Proteus vulgaris cells was used in the reduction of chloropyruvic acid to D-(S)-chlorolactic acid. A synthetic electron mediator 1,1'-carbamoylmethylviologen (CAV) was used to transfer electrons to HVOR. Three different methods for regenerating the mediator were evaluated: (1) electrochemically driven reduc
We have identified and characterized the temporal and spatial regulation of a plasma membrane arabinogalactan protein epitope during development of the aerial parts of oilseed rape using the monoclonal antibody JIM8. The JIM8 epitope is expressed by the first cells of the embryo and by certain cells in the sexual organs of flowers. During embryogenesis, the JIM8 epitope ceases to be expressed by t
Mass transfer limitations were studied in enzyme preparations of α- chymotrypsin made by deposition on different porous support materials such as controlled pore glasses, Celite, and polyamides of different particle sizes. It is the onset of mass transfer limitations that determines the position of the activity optimum with respect to enzyme loading on each support. The evidence of various experim
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
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
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
