The major isozyme of rat cardiac glutathione transferases. Its correspondence to hepatic transferase X

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Abstract
1. A major isozyme of rat heart glutathione transferase was purified to homogeneity by Sephadex G-200 gel filtration, ammonium sulfate precipitation, CM-cellulose chromatography and affinity chromatography on S-hexylglutathione-linked Sepharose 6 B. 2. The purified isozyme was a dimer with an apparent relative molecular mass of 50000 composed of two Yb-size subunits (Mr = 26500). The isozyme is immunologically related to rat liver glutathione transferase X and 3-3, especially closely to transferase X, and no immunological cross-reactivity with subunits 1 and 2 of hepatic glutathione transferases was observed. The isoelectric point (pI = 6.9) of the isozyme was identical with and the substrate specificity was very similar to transferase X. Thus, the cardiac near-neutral isozyme is considered to be identical to glutathione transferase X recognized in rat liver. 3. The amount of this near-neutral isozyme estimated to be present in heart tissue is 70 .mu.g/g. The isozyme has relatively high activities towards .alpha.,.beta.-unsaturated carbonyl compounds such as trans-4-phenyl-3-buten-2-one and trans-4-hydroxynon-2-enal. The latter is a cytotoxic product resulting from lipid peroxidation of polyunsaturated fatty acids and the cardiac isozyme may play a physiologically significant role with glutathione conjugation of this compound. 4. In addition to the near-neutral isozyme, acidic forms with isoelectric points of 4.9, 5.2 and 5.5 were partially purified; some of them are considered to consist of subunits immunologically related to transferase X.