Do the major human glutathione S-transferases have fatty acid ethyl ester synthase activity?

Two fatty acid ester (FAEE) synthase isoenzymes purified from human myocardium were reported to be glutathione S-transferases (GST) [(1989) Proc. Natl. Acad. Sci. USA 86, 4470–4473; and (1989) J. Clin. Invest. 84, 1942–1946]. In the present study, the FAEE synthase activity of several purified and well characterized human GSTs were examined with ethanol and [ 14C]oleic acid as substrates. Three isoenzymes, GST1, GST2 and GST3 which are members of the evolutionary classes μ, α and π, respectively, were studied and failed to show any significant synthesis of FAEE after 45 min incubation at 37°C, FAEE synthase activity and GST3 activity in human placental extracts can be readily separated by ion exchage chromatography on DEAE cellulose. Thus the results show that FAEE synthase activity is not a feature of the major GSTs found in human tissues. The two FAEE synthase isoenzymes isolated by Bora et al. may have been co-purified with GST isoenzymes of these FAEE synthases may be members of the GST super family that have low specific activity in conventional GST assays and have not been previously described.