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Two different immobilisation techniques for lipases were investigated: adsorption on to Accurel EP-100 and deposition on to Celite. The specific activities were in the same order of magnitude, 2.9 (μmol min -1 mg protein) when Celite was used as support and 2.3 (μmol min -1 mg -1 protein) when Accurel EP-100 was used as support,
Enzymatic synthesis of cetyl palmitate was performed in a solvent-free system at 65 °C using immobilized Candida antarctica lipase. Batch reactions at controlled water activity showed that the yield could be increased from 88.8 to 99.1% by decreasing the water activity from 1 to 0.05. A continuous reactor configuration was constructed, where two tubular reactors were run in sequence with a separat
(S)-Hydroxynitrile lyases from Hevea brasiliensis, Manihot esculenta, and Sorghum bicolor and (R)-hydroxynitrile lyase from Prunus amygdalus have been used as biocatalyst for the enantiospecific addition of hydrogen cyanide to aldehydes in organic solvents. The effects of the reaction parameters on the enzymatic reaction rate and product enantiomeric excess (e.e.) are presented. The reaction rate
Immobilised 1,3-specific lipase from Rhizopus arrhizus was used as catalyst for the esterification of dl-glycero-3-phosphate and fatty acid or fatty acid vinyl ester in a solvent-free system. With lauric acid vinyl ester as acyl donor, a(w)<0.53 favored the synthesis of lysophosphatidic acid (1-acyl-rac-glycero-3-phosphate, LPA1) and the spontaneous acyl migration of the fatty acid on the molecule
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
