Abstract: The present invention relates to a DNA fragment containing a nucleotide sequence that encodes an amino acid sequence of esterase, said esterase asymmetrically hydrolyzing carboxylic acid esters represented by the formula (I); ##STR1## (wherein R.sub.1 is alkyl, aralkyl or aryl, R.sub.2 and R.sub.3 are alkyl, and n is 1 or 2) an esterase encoded by the DNA fragment, a recombinant plasmid containing the DNA fragment, a microorganism transformed with the recombinant plasmid and methods of producing optically active carboxylic acids and their enantiomeric esters.

Abstract: N-(3-acetylthio-2-D-methylpropionyl)-L-proline useful as a precursor of captopril, one of antihypertensive agents, is prepared by allowing thioacetic acid to react with methyl methacrylate to prepare racetalc methyl 3-acetylthio-2-DL-methylpropionate, contacting the propionate with cells of, for example, Pseudomonas in order to effect biological and asymmetric hydrolysis, extracting 3-acetylthio-D-2-methylpropionic acid and allowing the acid to react with L-proline.

Abstract: An L-proline derivative represented by: ##STR1## wherein R.sub.2 represents a lower alkyl group is prepared by reacting L-proline with a D-.alpha.-alkyl-.beta.-acylthiopropionic acid halide, ##STR2## wherein R.sub.1 represents an acyl group, X represents a halogen atom and R.sub.2 has the same meaning as defined above. The halide is added to an aqueous medium containing L-proline and a condensation agent for deacidification. The halide and L-proline are reacted while the reaction temperature and pH are maintained at 12.degree. C. or lower and within a range of 10.5-11.5, whereby a compound represented by: ##STR3## wherein R.sub.1 and R.sub.2 have the same meanings as defined above is obtained. The resulting compound is then subjected to deacylation under strong alkaline conditions without being isolated from the reaction mixture, thereby yielding the target L-proline derivative.

Abstract: The present invention relates to a DNA fragment containing a nucleotide sequence that encodes an amino acid sequence of esterase, said esterase asymmetrically hydrolyzing carboxylic acid esters represented by the formula (I); ##STR1## (wherein R.sub.1 is alkyl, aralkyl or aryl, R.sub.2 and R.sub.3 are alkyl, and n is 1 or 2) an esterase encoded by the DNA fragment, a recombinant plasmid containing the DNA fragment, a microorganism transformed with the recombinant plasmid and methods of producing optically active carboxylic acids and their enantiomeric esters.

Abstract: Process for racemizing an optically active carboxylic acid ester of the formula (1): ##STR1## wherein R.sub.1 is alkyl, aralkyl or aryl, R.sub.2 and R.sub.3 independently are alkyl, and n is 1 or 2, which comprises contacting the compound of the formula (1) with an amine compound.

Abstract: A method for culturing cells by supplying oxygen to a culture medium through a multilayer composite membrane consisting of a porous layer(s) and a nonporous layer(s) having a thickness of less than 10 micrometers laminated one after the other. By using this multilayer composite membrane for supplying oxygen to the culture medium, oxygen can be supplied to the culture medium and/or the culture broth without causing foaming in the culture medium, cell growth inhibition or reduction in productivity of cellular products.

Abstract: A process for the preparation of an organic ester of ascorbic acid or erythorbic acid represented by the general formula (II) or (III): ##STR1## wherein R.sub.1 is alkyl, aralkyl, or aryl, by reacting ascorbic acid or erythorbic acid with an organic acid or an ester thereof of the general formula (I) :R.sub.1 COOR.sub.2 (I)wherein R.sub.1 is as defined above and R.sub.2 is hydrogen, methyl, ethyl or propyl, in an organic solvent in the presence of an ester hydrolase.

Abstract: A process for the preparation of an organic ester of ascorbic acid or erythorbic acid represented by the general formula (II) or (III): ##STR1## wherein R.sub.1 is alkyl, aralkyl, or aryl, by reacting ascorbic acid or erythorbic acid with an organic acid or an ester thereof of the general formula (I):wherein R.sub.1 is as defined above and R.sub.2 is hydrogen, methyl, ethyl or propyl, in an organic solvent in the presence of an ester hydrolase.

Abstract: High molecular weight hyaluronic acid can be efficiently produced by incorporating one or more compounds having at least one aromatic ring to which one or more hydroxyl groups are attached into a medium for producing hyaluronic acid by a bacterium capable of producing hyaluronic acid. By using this method, a sufficient amount of hyaluronic acid can be easily obtained without decomposing the high molecular structure of hyaluronic acid so that the process for isolating and purifying hyaluronic acid from the medium can be simplified.

Abstract: A process for treating contaminated water containing BOD sources and nitrogen sources, which comprises supplying oxygen or oxygen-containing gas from one side of a gas-permeable membrane to grow microorganisms including aerobic bacteria and anaerobic bacteria on the other side of the gas-permeable membrane, and performing decomposition of the BOD sources and nitrification and denitrification simultaneously by the action of these microorganisms. Especially good results are obtained when a membrane composed of porous hollow fibers is used as the gas-permeable membrane.

Abstract: Organic carboxylic acid ester represented by the formula (II): ##STR1## wherein R.sub.1 is an alkyl, an aralkyl or an aryl group; R.sub.2 is an alkyl group; R.sub.3 is an alkyl group; n is 1 or 2, are synthesized in racemic form, and then the acid ester (II) is treated with a source containing enzyme capable of rearranging with or without asymmetrically hydrolyzing ester bond until either a d-form or 1-form optically active carboxylic acid ester represented by the formula (II) with or without the antipode acid thereof is produced.

Abstract: Waste water containing organic pollutants is purified by biological treatment with aerobic microorganisms supported on hollow fibers having microporous walls through which oxygen is supplied to the microorganisms.