Novel Theta Class Glutathione S-Transferases Yrs-Yrs′ and Yrs′-Yrs′ in Rat Liver Cytosol: Their Potent Activity Toward 5-Sulfoxymethylchrysene, a Reactive Metabolite of the Carcinogen 5-Hydroxymethylchrysene

Abstract

Two novel 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 (Hiratsuka, A. et al., J. Biol. Chem, 265, 11973 (1990)) 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 separated from Yrs by reverse partition HPLC, but identical to Yrs in the first 37 N-terminal amino acid sequence. 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 2-chloro-2,4-dinitrobenzene. However, they showed potent activities toward the reactive sulfate ester of the carcinogen, 5-hydroxymethylchrysene. GSTs Yrs-Yrs and Yrs′-Yrs′ showed much higher GSH peroxidase activities toward arachidonate hydroperoxide than did rat liver alpha class GST Ya-Ya.