Purification and characterization of the individual glutathione S-transferases from sheep liver

The glutathione S-transferases (EC 2.5.1.18) have been purified to electrophoretic homogeneity from 105,000g supernatant of sheep liver homogenate by employing a combination of gel filtration on Sephadex G-150 and affinity chromatography on S-hexylglutathione-linked Sepharose-6B columns. Approximately 70% of the original glutathione S-transferase activity toward 1-chloro-2,4-dinitrobenzene and glutathione peroxidase activity toward cumene hydroperoxide could be recovered by this purification method. Of particular importance in developing this procedure was the fact that the enzyme preparation obtained after affinity column chromatography represented all the isozymes of sheep liver glutathione S-transferases. Further purification by CM-cellulose and DEAE-cellulose column chromatography resolved the glutathione S-transferases into seven distinct cationic isozymes designated C-1, C-2, C-3, C-4, C-5, C-6, and C-7 and five overlapping anionic transferases designated A-1, A-2, A-3, A-4, and A-5, respectively, in the order of their elution from the ion-exchange columns. The sodium dodecyl sulfate SDS-gel electrophoretic data on subunit composition revealed that cationic enzymes are composed of two subunits with an identical Mr of 24,000 whereas a predominant subunit with Mr of 26,000 was observed in all anionic isozyme peaks except A-1. Cationic isozymes accounted for approximately 98% of the total peroxidase activity associated with the glutathione S-transferase whereas only A-1 of the anionic isozymes displayed some peroxidase activity. Isozyme C-4 was found to be the most abundant glutathione S-transferase in the sheep liver. Characterization of the individual transferases by their specificity toward a number of selected substrates, subunit composition, and isoelectric points showed some similarities to those patterns for human liver glutathione S-transferases.