Purification and Characterization of P-52 (Glutathione S-Transferase-P or 7-7) from Normal Liver and Putative Preneoplastic Liver Nodules

A previous study from our laboratory (L. C. Eriksson et al. , Biochem. Biophys. Res. Commun., 117: 740–745, 1983) revealed that a cytosolic polypeptide of approximate M r 21,000 (designated P-21) was markedly elevated in amount in hepatocyte nodules induced by six different regimens. The molecular weight of this polypeptide, subsequently revised to approximately 26,000, was redesignated P-26 and was identified (T. H. Rushmore et al. , Biochem. Biophys. Res. Commun., 143: 98–103, 1987) as a subunit of a placental form of glutathione S -transferase (K. Sato et al. , Gann 75: 199–202, 1984), also named glutathione S -transferase 7-7 (H. Jensson et al. , FEBS Lett., 187: 115–120, 1985). We describe here a convenient method for purifying relatively large amounts of P-26 from hepatocyte nodules involving the sequential use of affinity chromatography on S -hexyl glutathione-Sepharose 4B, CM-Sephadex, and DEAE-Sephacel. Evidence is presented that P-26 exists as a dimer of approximate M r 52,000 (P-52). Analyses by two-dimensional electrophoresis have indicated that the subunits of M r 26,000 may consist of five separate charged isomers. Investigations using appropriate antisera and analysis by amino acid sequencing have provided additional confirmation that P-52 is probably identical to rat placental glutathione S -transferase. Antibodies to P-52 are proving to be useful as a marker of new cell populations that appear regularly during hepatocarcinogenesis.