The role of human glutathione S-transferases hGSTA1-1 and hGSTA2-2 in protection against oxidative stress

In order to elucidate the protective role of glutathione S-transferases (GS Ts) against oxidative stress, we have investigated the kinetic properties o f the human alpha-class GSTs, hGSTA1-1 and hGSTA2-2, toward physiologically relevant hydroperoxides and have studied the role of these enzymes in glut athione (GSH)-dependent reduction of these hydroperoxides in human liver. W e have cloned hGSTA1-1 and hGSTA2-2 from a human lung cDNA library and expr essed both in Escherichia coli. Both isozymes had remarkably high peroxidas e activity toward fatty acid hydroperoxides, phospholipid hydroperoxides, a nd cumene hydroperoxide. In general, the activity of hGSTA2-2 was higher th an that of hGSTA1-1 toward these substrates. For example, the catalytic eff iciency (k(cat)/K-m) of hGSTA1-1 for phosphatidylcholine (PC) hydroperoxide and phosphatidylethanolamine (PE) hydroperoxide was found to be 181.3 and 199.6 s(-1) mM(-1), respectively, while the catalytic efficiency of hGSTA2- 2 for PC-hydroperoxide and PE-hydroperoxide was 317.5 and 353 s(-1) mM(-1), respectively. Immunotitration studies with human liver extracts showed tha t the antibodies against human alpha-class GSTs immunoprecipitated about 55 and 75% of glutathione peroxidase (GPx) activity of human liver toward PC- hydroperoxide and cumene hydroperoxide, respectively. GPx activity was not immunoprecipitated by the same antibodies from human erythrocyte hemolysate s. These results show that the alpha-class GSTs contribute a major portion of GPx activity toward lipid hydroperoxides in human liver. Our results als o suggest that GSTs may be involved in the reduction of 5-hydroperoxyeicosa tetraenoic acid, an important intermediate in the 5-lipoxygenase pathway. ( C) 1999 Academic Press.