The hepatic glutathione transferases of the male little skate, Raja erinacea

Abstract

Five cytosolic glutathione transferases were isolated from the liver of the male little skate, Raja erinacea, a marine elasmobranch. They were designated E-1 through E-5 in order of their elution from a DEAE-cellulose column with a 0 to 100 mM KCl gradient in 0.01 M Tris (pH 8.0). Each eluted peak of glutathione transferase activity, after concentration, was applied to an affinity column prepared by reaction of epoxy-activated Sepharose 6B with glutathione (GSH). Elution of the various glutathione transferases from this column with GSH resulted in the further purification of each enzyme; the major glutathione transferase, E-4 and E-1, were purified to apparent homogeneity by this procedure. Skate glutathione transferase E-4 is dimeric and the subunits are either very similar or identical in molecular weight (about 26 000 daltons). Enzymes E-2 through E-5 were acidic proteins (pI < 7.0) and had high specific glutathione transferase activity (0.3–12 μmol/min/mg protein) with benzo[ a]pyrene 4,5-oxide (BPO) as substrate, whereas the other enzyme (E-1) had low activity (0.01 μmol/min/mg) with BPO and a basic pI (>9.5). Bilirubin and hematin, non-substrate ligands, bound tightly to homogenous E-4, with dissociation constants in the micromolar range.