ALPHA-CLASS ISOZYMES OF GLUTATHIONE-S-TRANSFERASE IN RAT-LIVER CYTOSOL POSSESS GLUTATHIONE-PEROXIDASE ACTIVITY TOWARD PHOSPHOLIPID HYDROPEROXIDE

Selenium-independent enzymes, found in the liver cytosol of selenium-d eficient rats, that are capable of reducing dilinoleoyl phosphatidylch oline hydroperoxide in the presence of reduced glutathione [Guan et al ., (1995) Biochem. Mol. Biol. Int., 37, 1103-1110] were purified to ho mogeneity by use of successive chromatography on glutathione affinity and Mono P columns. The molecular weight of the purified protein was e stimated by gel filtration to be approximately 50 kDa. Upon isoelectri c focusing, the purified preparation showed two protein bands having p I values of 8.6 and 8.8. Both proteins had reactivity against both 1-c hloro-2,4-dinitrobenzene and dilinoleoyl phosphatidylcholine hydropero xide in the presence of reduced glutathione. Each of them consisted of two subunits having molecular weights of 24.3 kDa and 26 kDa, as esti mated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Th e large subunit was identified as rat glutathione S-transferase (GST) 2 (Yc subunit) based on the amino-terminal amino acid sequence analysi s. The small subunit was considered to be most probably rat GST 1 (Ya subunit). From these results, we conclude that the basic a-class isozy mes of GST in rat liver cytosol possess glutathione peroxidase activit y toward phospholipid hydroperoxide.