STEREOSELECTIVITY OF LIPASES : Stereoselective hydrolysis of triglycerides by gastric and pancreatic lipases

Abstract

In the present study, porcine pancreatic lipase (PPL), rabbit gastric lipase (RGL) and human gastric lipase (HGL) stereospecificity towards chemically like, but sterically non equivalent ester groups within onesingle triglyceride molecule was investigated. Lipolysis reactions were carried out on synthetic trioctanoin ortriolein, which are homogenous, prochiral triglycerides, chosen as models for physiological lipase substrates. Diglyceride mixtures resulting from lipolysis were derivatized with optically active R-(+)-1-phenylethylisocyanate, to give diastereomeric carbamate mixtures, which were further separated by HPLC. Resolution of diastereomeric carbamates gave enantiomeric excess values, which reflect the lipases stereobias and clearly demonstrate the existence of a stereopreference by both gastric lipases for the sn-3 position. The stereoselectivity of HGL and RGL,expressed as the enantiomeric excess percentage, was 54% and 70% for trioctanoin and 74% and 47% fortriolein, respectively. The corresponding values with PPL were 3% in the caseof trioctanoin and 8% in that of triolein. It is worth noting that RGL, unlike HGL, became morestereoselective for the triglyceride with shorter acyl chains (trioctanoin). This is one of the moststriking catalytic differences observed between these twogastric lipases.