Purification of rat liver plasma membrane glutathione transferase

Glutathione transferases purified from plasma membrane and microsomal fractions from rat liver share similar enzymic properties. The activity of both proteins with 1-chloro-2,4-dinitrobenzene can be stimulated about 10-15-fold by N-ethylmaleimide. No activation is observed using p-nitrobenzylchloride as a substrate. The enzymes are immunologically related as indicated by Western-blot analysis using antibodies against the microsomal glutathione transferase or against a synthetic peptide corresponding to the amino acid positions 55-64 of microsomal glutathione transferase. Isolated plasma membrane and microsomal glutathione transferases possess the same amino-terminal amino acid sequence and digestion with different proteases results in identical fragment patterns as displayed by SDS/PAGE. These data suggest that plasma membrane and microsomal glutathione transferase are identical proteins.