A LIPID-COATED LIPASE AS AN ENANTIOSELECTIVE ESTER SYNTHESIS CATALYSTIN HOMOGENEOUS ORGANIC-SOLVENTS

A lipid-coated lipase was prepared, in which hydrophilic head groups o f lipids interact with the hydrophilic surface of the enzyme and lipop hilic alkyl chains extend away from its surface and solubilize the enz yme in hydrophobic organic solvents. Enantioselective esterification o f(R)- or (S)-1-phenylethanol with aliphatic acid was studied in the pr esence of the lipid-coated lipase, solubilized homogeneously in organi c solvents, by varying lipase origin, coating lipid molecules, reactio n media, and substrate structures. The lipid-coated lipase prepared fr om the glycolipid (1) and lipase B from Pseudomonas fragi 22-39B showe d both a high catalytic activity and enantioselectivity for the esteri fication of (R)-1-phenylethanol with long-chain aliphatic acid in dry isooctane, relative to other enzyme systems such as poly(ethylene glyc ol)-grafted lipase, lipase powder directly dispersed in organic solven ts, and a water/organic emulsion system. The coating lipids are found to not affect the enzyme reactions and to act simply as lipophilic tai ls in organic media. The lipid-coated lipase is suitable for studying the reaction mechanism of the enzyme in organic solvents since the rea ction is carried out in homogeneous media. It has been found in studyi ng Michaelis-Menten kinetics that the lipid-coated lipase (or native l ipase) has two binding sites for long-chain aliphatic acids and for en antiomorphic secondary alcohols having a small methyl and a large phen yl side chain. Aliphatic acid is bound first and then alcohol. The ena ntioselectivity of the esterification is determined by the nucleophili c attack of the enantiomorphic alcohol, but not in the binding process of the enantiomorphic alcohol.