Rainbow trout liver microsomal lipid peroxidation. The effect of purified glutathione peroxidase, glutathione S-transferase and other factors.

Glutathione peroxidase (glutathione: hydrogen-peroxide oxidoreductase, EC 1.11.1.9) was purified approximately 600-fold from rainbow trout liver soluble fraction and its activity in the NADPH microsomal lipid peroxidation system tested. The enzyme has an approximate molecular weight of 100 000, contains four subunits and four atoms of selenium per mol protein. No selenium-independent glutathione peroxidase activity could be attributed to glutathione S-transferase (EC 2.5.1.18) in trout liver. Glutathione peroxidase together with glutathione (GSH) did not provide any additional protection in the in vitro liver microsomal lipid peroxidation system over and above that provided by GSH alone. Microsomal lipid peroxidation was, however, reduced by a partially purified glutathione S-transferase together with GSH. The protection provided by dialysed liver cytosol in this system was not GSH-dependent, showing that other factors in addition to glutathione S-transferase are involved. Of other possible factors, vitamin E reduced lipid peroxidation in this system. Concentrations of vitamin E in microsomes before and after peroxidation in vitro indicated that protective cytosolic factor(s) act prior to the termination of the free radical chain reactions effected by vitamin E. A GSH-dependent protective factor was present in microsomal protein, malondialdehyde formation in the in vitro microsomal system being markedly reduced in the presence of 5 mM GSH but not significantly lowered by 1 mM GSH.