The stereoselectivity of four hepatic glutathione S-transferases purifed from a marine elasmobranch ( Raja erinacea) with several K-region polycyclic arene oxide substrates

Abstract

Product analysis by HPLC demonstrated that three hepatic cytosolic glutathione S-transferases of little skate (E-2, E-3 and E-4) were highly stereoselective, if not stereospecific, for thiol reaction at the R-configured oxirane carbons of four K-region arene oxides; pyrene 4,5-oxide, (±)-benz[ a]-anthracene 5,6-oxide, (±)-benzo[ a]pyrene 4,5-oxide and phenanthrene 9,10-oxide. A fourth transferase, E-5, exhibited no stereopreference with pyrene 4,5-oxide or phenanthrene 9,10-oxide. Immunological and electrophoretic evidence has shown that the three enzymes exhibiting stereospecificity have a common subunit which is absent from enzyme E-5. The high stereoselectivity of the three enzymes E-2, E-3, and E-4 was accompanied by effective catalysis of the reaction of GSH with these K-region epoxides, for example, the calculated turnover number for E-4 with benzo[ a]pyrene 4,5-oxide was 550.