Glutathione peroxidase II of guinea pig liver cytosol: Relationship to glutathione S-transferases

GSH peroxidase II activity is not associated with all GSH- S-transferase (EC 2.5.1.18) proteins. In guinea pig liver GSH peroxidase II (nonseleno and specific for organic hydroperoxides) is associated almost entirely with GSH- S-transferase peak aa and a smaller peak designated aa′. Transferase a shows a slight peroxidase activity, transferase b is absent, and transferase c has no peroxidase activity. GSH peroxidase II of guinea pig liver has an isoelectric point of 8.9 and a molecular weight of 45,000. It consists of two subunits of similar size (26,000). The GSH peroxidase II and the GSH- S-transferase activities of transferase aa have not been resolved into separate proteins and presumably reside in the same protein. In rat liver GSH peroxidase II activity is present with the highest specific activity in GSH- S-transferase AA. There is no AA′. Transferase B also shows peroxidase activity. Transferases A and C show low but measurable peroxidase activity. Transferase peak E shows peroxidase activity, but it is contaminated by large amounts of GSH peroxidase I (EC 1.11.1.9), recognized by its activity on H 2O 2.