SUBUNIT YA-SPECIFIC GLUTATHIONE-PEROXIDASE ACTIVITY TOWARD CHOLESTEROL 7-HYDROPEROXIDES OF GLUTATHIONE S-TRANSFERASES IN CYTOSOLS FROM RAT-LIVER AND SKIN
A. Hiratsuka et al., SUBUNIT YA-SPECIFIC GLUTATHIONE-PEROXIDASE ACTIVITY TOWARD CHOLESTEROL 7-HYDROPEROXIDES OF GLUTATHIONE S-TRANSFERASES IN CYTOSOLS FROM RAT-LIVER AND SKIN, The Journal of biological chemistry, 272(8), 1997, pp. 4763-4769
Dermal 7 alpha- and 7 beta-hydroperoxycholest-5-en-3 beta-ols (cholest
erol 7 alpha- and 7 beta-hydroperoxides), regarded as good aging marke
rs in the rat (Ozawa, N., Yamazaki, S., Chiba, K., Aoyama, H., Tomisaw
a, H., Tateishi, M., and Watabe, T. (1991) Biochem. Biophys. Res. Comm
un. 178, 242-247), were reduced in the presence of glutathione (GSH) w
ith concomitant formation of GSSG by cytosol from rat liver in which n
o detectable level of the hy droperoxides had been demonstrated to occ
ur. The GSH peroxidase (GSH Pr) activity toward the toxic steroid hydr
operoxides was exerted to almost the same extent by both Alpha-class G
SH 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 ra
t liver and a Pi-class GST, Yp-Yp, from rat kidney showed any apprecia
ble GSH Pr activity toward the hydroperoxides. The subunit Ya-bearing
GSTs and Se GSH Pr purified from rat liver cytosol showed marked diffe
rences in apparent specific activity toward the cholesterol hydroperox
ides (GSTs Ya-Ya > Ya-Yc much greater than Se-GSH Pr). However, a kine
tic study indicated that Se-GSH Pr had a higher affinity for steroid h
ydroperoxides 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 h
ad no GST bearing the subunit Ya but contained only a very low concent
ration of Se GSH Pr, possibly resulting in the accumulation of cholest
erol 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 isolate
d, purified to homogeneity, and identified with the corresponding GSTs
from liver and kidney. The GSTs accounted for 0.23% of total skin cyt
osolic 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.