Abstract: A process for preparing an optically active mercapto compound having asymmetrical centers having the formula: ##STR1## in which R.sub.1 represents an alkyl group, R represents a hydrogen atom or an alkyl group, C* represents an asymmetric carbon, n represents the value of 1 or 2, is disclosed. The process involves the reaction of a cultured microorganism having the ability of asymmetrically hydrolyzing ester bonds of the raw material, thus eliminating the need for protecting free mercapto groups which are unstable in the reaction conditions. The optically active mercapto compound is useful as a raw material for producing a compound having medicinal effects such as antihypertensive activity.

Abstract: A porous gel containing an immobilized enzyme is prepared by mixing an aqueous solution of polyvinyl alcohol having a saponification degree of not lower than 95 mol% and an average polymerization degree of not lower than 1,000, with an enzyme or enzyme-producing cell, and activated carbon powder, pouring the mixture into a container of any desired form, gelating and molding the mixture by dehydrating it up to a dehydration ratio of not lower than 50%, immersing the resulting molding in water, and drying the immersed molding. Preferably, dehydrating is by leaving the mixture to stand at room temperature or a temperature of from 30.degree. C. to 40.degree. C. The enzyme or enzyme-producing cell may be mixed with or adsorbed on an inorganic or organic carrier. The dried molding may be granulated.