MASS-SPECTROMETRIC ANALYSIS OF RAT-LIVER CYTOSOLIC GLUTATHIONE S-TRANSFERASES - MODIFICATIONS ARE LIMITED TO N-TERMINAL PROCESSING

Cytosolic glutathione S-transferases (GSTs) from rat livers were purif ied using an S-hexylglutathione affinity column. The GST subunits were resolved by reverse-phase HPLC and their molecular masses were determ ined by electrospray mass spectrometry. The major hepatic GSTs detecte d were subunits 1, 1', 2, 3 and 4, with molecular mass of 25520, 25473 , 25188, 25782 and 25571 Da respectively. Subunits 6, 7 and 10 are min or components, with molecular mass of 25551, 23308 and 25211 Da respec tively. Alternatively, the hepatic GSTs were purified using a glutathi one affinity column. Subunits 1, 1', 2, 8 and 10 were eluted from this column with GSSG, the oxidized form of glutathione. Subunit 8 has a m olecular mass of 25553 Da. The remaining proteins on the glutathione a ffinity column were removed with glutathione and S-hexylglutathione, S ubunits 2, 3, 4 and 6 could be detected in the eluate. We could not de tect any significant difference in molecular mass between GSTs isolate d from male and female rat livers. Cytosolic GSTs were isolated from l ivers of buthionine sulphoximine-treated female rats for MS analysis. The molecular masses obtained were identical to those determined for t he controls.