A GROUP OF NOVEL GLUTATHIONE-S-TRANSFERASE ISOZYMES SHOWING HIGH-ACTIVITY TOWARDS 4-HYDROXY-2-NONENAL ARE PRESENT IN BOVINE OCULAR-TISSUES

Recently, a mouse glutathione S-transferase (GST) isozyme, mGSTA4-4, w hich belongs to a distinct group of GSTs has been characterized in our laboratory. During the present studies, Western blot analyses of bovi ne ocular tissues using the antibodies raised against the recombinant mGSTA4-4 obtained by expression in Escherichia coli revealed that the orthologs of mGSTA4-4 were present in cornea, retina, iris-ciliary bod y and sclera, but absent in lens. These novel GST isozymes of bovine o cular tissues were purified by immunoaffinity chromatography using the antibodies against rec-mGSTA4-4 and were designated as bGST 5.8 (thei r pI value being 5.8). Amino acid sequences of CNBr fragments of bGST 5.8 from cornea, sclera, retina and iris-ciliary body showed high degr ee of primary structure homologies with the corresponding regions of m GSTA4-4 indicating these bovine GST isozymes were distinct from the a, mu and pi group GSTs and were the newest members of the group of GSTs to which mGSTA4-4 belongs. There were significant differences among t he amino acid sequences of bGST 5.8 of cornea and iris-ciliary body an d retina suggesting presence of at least two closely related genes at bGST 5.8 locus, bGST 5.8 isozymes showed high activity toward 4-HNE (f our-to-five-fold higher than that towards 1-chloro-2,4-dinitrobenzene) , expressed GSH-peroxidase activity towards fatty acid hydroperoxides and phospholipid hydroperoxides, and showed GSH-conjugating activity t owards fatty acid epoxides suggesting that these isozymes may play an important role in protection mechanism against the endogenous toxicant s formed during lipid peroxidation.