Independent segregation of glutathione S-transferase and fatty acid ethyl ester synthase from pancreas and other human tissues

Abstract

Glutathione S-transferase (GST) isoenzymes of human pancreas were purified, characterized and evaluated for their possible role in the metabolism of ethanol. Human pancreas has at least two GST isoenzymes belonging to the Alpha class (pI 8.8 and 8.1), one belonging to the Mu class (pI 6.4) and one belonging to the Pi class (pI 4.9). During the purification of GSTs from pancreas as well as from heart, liver, lung, brain and muscle, the fatty acid ethyl ester synthase (FAEES) activity was monitored in order to evaluate the role of GSTs in metabolism of ethanol, as suggested in earlier studies. Both t.l.c. and h.p.l.c. were used to identify ethyl oleate in reaction mixtures to monitor FAEES activity. During the purification of GSTs with the use of affinity chromatography on GSH linked to epoxy-activated Sepharose 6B, FAEES and GST activities from each of these tissues segregated independently. Purified GST isoenzymes from these tissues did not exhibit any FAEES activity. Antibodies raised against Pi-class GST, as expected, immunoprecipitated most of the GST activity of brain and heart without precipitating FAEES activity. These results suggest that human GST isoenzymes belonging to the Alpha, Mu and Pi classes do not express FAEES activity. The independent segregation of GST and FAEES activities was further demonstrated by monitoring GST activity during the purification of FAEES from pancreas. It was found that purified FAEES had no GST activity towards 1-chloro-2,4-dinitrobenzene and a number of other electrophilic substrates. Results of these studies demonstrate that FAEES and GSTs are distinct proteins.