Mouse liver glutathione S-transferases. Biochemical and immunological characterization

Abstract

Three major forms of cytosolic glutathione S-transferase (designated F1, F2, and F3 transferases according to increasing isoelectric points) were purified to homogeneity from liver of DBA/2J mice, primarily by CM-cellulose and hydroxylapatite chromatography. The purified enzymes were shown to have specific activities of 104, 281, and 143 units/mg, respectively, when assayed with 1 mM each of 1-chloro-2,4-dinitrobenzene and reduced glutathione. Antisera against these three forms of mouse transferase were raised separately in rabbits. F1 and F2 transferases showed complete immunological identity either by double immunodiffusion or enzyme immunoinactivation tests. No cross-reactivity was observed between the antisera to F1 (or F2) transferase an F3 transferase or between the antisera to F3 transferase and F1 (or F2) transferase. F1 and F2 transferases were shown to be homodimers with an identical molecular weight of 44,000 +/- 1,000, whereas F3 transferase has a dimeric molecular weight of 51,000 +/- 2,000. The amino acid composition and tryptic peptide map of F1 transferase are similar to those of F2 transferase, but are distinct from those of F3 transferase. In addition to these major forms, a minor form of mouse transferase (F4) with a high isoelectric point (greater than 9.5) was shown to be a mixture of interconvertible isomers of F2 and F3 transferase. Different forms of mouse transferase were studied extensively with respect to their biochemical properties, including Michaelis constants, substrate specificity, thermal stability, and fluorometric ligand binding. The results of this study suggest great species variations regarding the multiple forms as well as the substrate specificity of this family of enzymes.