| Abstract: | The 13 forms of human liver glutathione S-transferases (GST) (Vander Jagt, D. L., Hunsaker, L. A., Garcia, K. B., and Royer, R. E. (1985) J. Biol. Chem. 260, 11603-11610) are composed of subunits in two electrophoretic mobility groups: Mr = 26,000 (Ha) and Mr = 27,500 (Hb). Preparations purified from the S-hexyl GSH-linked Sepharose 4B affinity column revealed three additional peptides at Mr = 30,800, Mr = 31,200, and Mr = 32,200. Immunoprecipitation of human liver poly(A) RNAs in vitro translation products revealed three classes of GST subunits and related peptides at Mr = 26,000, Mr = 27,500, and Mr = 31,000. The Mr = 26,000 species (Ha) can be precipitated with antisera against a variety of rat liver GSTs containing Ya, Yb, and Yc subunits, whereas the Mr = 27,500 species (Hb) can be immunoprecipitated most efficiently by antiserum against the anionic isozymes as well as a second Yb-containing isozyme (peak V) from the rat liver. The Mr = 31,000 band can be immunoprecipitated by antisera preparations against sheep liver, rat liver, and rat testis isozymes. Human liver GSTs do not have any subunits of the rat liver Yc mobility. Antiserum against the human liver GSTs did not cross-react with the Yc subunits of rat livers or brains in immunoblotting experiments. The human liver GST cDNA clone, pGTH1, selected human liver poly(A) RNAs for the Ha subunit(s) in the hybrid-selected in vitro translation experiments. Southern blot hybridization results revealed cross-hybridization of pGTH1 with the Ya, Yb, and Yc subunit cDNA clones of rat liver GSTs. This sequence homology was substantiated further in that immobilized pGTH1 DNA selected rat liver poly(A) RNAs for the Ya, Yb, and Yc subunits with different efficiency as assayed by in vitro translation and immunoprecipitation. Therefore, we have demonstrated convincingly that sequence homology as well as immunological cross-reactivity exist between GST subunits from several rat tissues and the human liver. Also, the multiple forms of human liver GSTs are most likely encoded by a minimum of three different classes of mRNAs. These results suggest a genetic basis for the subunit heterogeneity of human liver GSTs. |
