A polypeptide of Mr 26,000 and pI 6.7 that was markedly increased in rat livers bearing hyperplastic nodules (HNs) induced by chemical carcinogens was identified immunochemically as the subunit of neutral glutathione (GSH) transferase (GSHTase; RX:glutathione R-transferase, EC 2.5.1.18; also called GSH S-transferase) purified from placenta (GSHTase-P) and was demonstrated immunohistochemically to be localized in preneoplastic foci and HNs. In the present study, GSHTase-P has been purified from the HN-bearing liver, and the distribution and inducibility have been examined quantitatively using anti-GSHTase-P antibody. Elevation of GSHTase-P in the HN-bearing livers was also confirmed by in vitro translation of mRNAs isolated from the HN-bearing livers. The purified GSHTase-P was homogeneous in size but had two charge isomers on two-dimensional gel electrophoresis. In normal tissues, including liver, placenta, and fetal liver, the protein content of GSHTase-P was generally low but was significantly high in kidney and pancreas. In contrast, the amount of GSHTase-P in HN-bearing livers (primary hepatomas) and transplantable Morris hepatoma 5123D were several 10-fold higher than that in normal liver but were undetectably low in transplantable Yoshida ascites hepatoma AH 130. Different from ordinary drug-metabolizing enzymes, GSHTase-P was uninducible by administration of drugs and carcinogens prior to appearance of the preneoplastic foci and HNs. In addition, species specificity of GSHTase-P was low as it was crossreactive among rat, hamster, and human.Much attention has been focused on the morphological, histochemical, and biochemical properties of the preneoplastic cells such as enzyme-altered foci and hyperplastic nodules (HNs) induced at early stages of chemical hepatocarcinogenesis (1-5). Among (pre)neoplastic markers so far found, epoxide hydrase (6) tocarcinogenesis. In our studies of isozymic alterations during chemical hepatocarcinogenesis, especially of drugmetabolizing enzymes (7, 11-15), we observed by twodimensional gel electrophoretic analysis of the cytosolic proteins of the HN-bearing rat livers that a polypeptide of Mr 26,000 and pI 6.7 [designated polypeptide (26/6.7)] increased most markedly together with three other proteins. This polypeptide was identified immunochemically as the subunit of a neutral GSHTase that was purified from rat placenta. This placental form (GSHTase-P) was demonstrated to be localized in HNs and in foci positive for y-glutamyltransferase (GluTase; y-glutamyl transpeptidase, EC 2.3.2.2) (14).In the present study, GSHTase-P has been purified from HN-bearing rat livers, some chemical properties have been characterized, and the content of this protein in normal, preneoplastic, and neoplastic tissues and its inducibility in rat livers by drugs and carcinogens have been examined.MATERIALS AND METHODS Animals. Male Sprague-Dawley rats, weighing 150-160 g, were obtained from Charles River-Oriental Yeast (Tokyo).Chemicals. Chemicals were obtained as follows; diethylnitrosami...

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