REDUCING ACTIVITY TOWARD HYDROPEROXIDES OF RAT HEPATIC CLASS <I>THETA</I> GLUTATHIONE S-TRANSFERASES

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Two new theta class glutathione S-transferases (GSTs), designated Yrs-Yrs' and Yrs'-Yrs', were isolated from rat liver cytosol and purified to homogeneity. Polyclonal antibody raised against the previously reported theta class GST Yrs-Yrs cross-reacted with GSTs Yrs-Yrs' and Yrs'-Yrs'. These three theta class GSTs had different pI values and were separated by chromatofocusing. The enzyme subunit Yrs' was identical to Yrs in the first 37 N-terminal amino acid sequence and electrophoretic mobility, but separable from Yrs on a hydrophobic column by reverse partition HPLC. Like GST Yrs-Yrs, both GSTs Yrs-Yrs' and Yrs'-Yrs' were not retained on an S-hexyl-GSH affinity column and had little activity toward 1-chloro-2, 4-dinitrobenzene. However, they showed potent activities toward the reactive sulfate ester of the carcinogen, 5-hydroxymethylchrysene. GST Yrs-Yrs showed much higher GSH peroxidase activities toward hydroperoxides of endogenous polyunsaturated fatty acids than did rat liver alpha class GSTs. GST Yrs'-Yrs' showed a much higher activity only toward the arachidonate hydroperoxide than did alpha class GSTs. The linolate and linolenate hydroperoxides were poorer substrates for GST Yrs'-Yrs' than for the alpha class GSTs. The above fact strongly suggests that the theta class GSTs may play an important role in retarding the oxidative stress induced by hydroperoxides of polyunsaturated fatty acids derived by pospholipase A2 from phospholipid hydroperoxides formed in hepatic intracellular membranes.