Subunit Ya-specific glutathione peroxidase activity toward cholesterol 7-hydroperoxides of glutathione S-transferases in cytosols from rat liver and skin

Dermal 7 alpha- and 7 beta-hydroperoxycholest-5-en-3 beta-ols (cholesterol 7 alpha- and 7 beta-hydroperoxides), regarded as good aging markers in the rat (Ozawa, N., Yamazaki, S., Chiba, K., Aoyama, H., Tomisawa, H., Tateishi, M., and Watabe, T. (1991) Biochem. Biophys. Res. Commun. 178, 242-247), were reduced in the presence of glutathione (GSH) with concomitant formation of GSSG by cytosol from rat liver in which no detectable level of the hy droperoxides had been demonstrated to occur. The GSH peroxidase (GSH Pr) activity toward the toxic steroid hydroperoxides was exerted to almost the same extent by both Alpha-class GSH S-transferases (GSTs), Ya-Ya and Ya-Yc, and by selenium-containing GSH Pr (Se-GSH Pr) in rat liver cytosol. None of three Mu class GSTs, Yb1-Yb1, Yb1-Yb2, and Yb2-Yb2, and a Theta-class GST, Yrs-Yrs, from rat liver and a Pi-class GST, Yp-Yp, from rat kidney showed any appreciable GSH Pr activity toward the hydroperoxides. The subunit Ya-bearing GSTs and Se GSH Pr purified from rat liver cytosol showed marked differences in apparent specific activity toward the cholesterol hydroperoxides (GSTs Ya-Ya > Ya-Yc much greater than Se-GSH Pr). However, a kinetic study indicated that Se-GSH Pr had a higher affinity for steroid hydroperoxides than did the GSTs, so that Se GSH Pr could catalyze the reduction of lower concentrations of cholesterol 7-hydroperoxides with approximately equal V-max/K-m values to those by the GSTs. Rat skin had no GST bearing the subunit Ya but contained only a very low concentration of Se GSH Pr, possibly resulting in the accumulation of cholesterol 7-hydroperoxides in the skin but not in the liver. From rat skin cytosol, GSTs Yc-Yc, Yb1-Yb1, Yb1-Yb2, Yb2-Yb2, and Yp-Yp were isolated, purified to homogeneity, and identified with the corresponding GSTs from liver and kidney. The GSTs accounted for 0.23% of total skin cytosolic protein, and the most abundant isoform of skin GSTs was Yb2-Yb2, followed by Yc-Yc, Yp-Yp, Yb1-Yb1, and Yb1-Yb2 in decreasing order.