Identification of a satellite fatty acid ethyl ester synthase from human myocardium as a glutathione S-transferase

Abstract

Nonoxidative alcohol metabolism catalyzed by fatty acid ethyl ester (FAEE) synthases may contribute to extrahepatic injury resulting from alcohol abuse. Unlike rabbit myocardial FAEE synthase, that from human heart has a satellite minor synthase (I) eluting from DEAE cellulose at a conductivity of 5 mS. Synthase I was puriied 1,118-fold to homogeneity by sequential gel permeation, hydrophobic interaction, and Superose-12 fast-protein liquid chromatographies. SDS-PAGE showed a single polypeptide with a molecular mass of 26 kD and gel permeation chromatography indicated a molecular mass of 52 kD for the active enzyme. Homogeneous synthase I catalyzed ethyl ester synthesis at highest rates with unsaturated octadecanoic fatty acid substrates. The amino acid composition of synthase I was highly homologous to that of human myocardial major synthase, recently identified as an acidic glutathione (GSH) S-transferase. Antibody raised against homogeneous human heart major synthase cross-reacted with the 26-kD synthase I. FAEE synthase co-chromatographed with GSH S-transferase on DEAE cellulose, Sephadex G-100 and S-hexylglutathione agarose, and also displayed GSH S-transferase activity in catalyzing the conjugation of GSH with nitrobenzene-containing carcinogens. Thus, human myocardium contains a satellite peak of FAEE synthase activity and it is a neutral GSH S-transferase.