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, which belongs to a distinct group of GSTs has been characterized in our laboratory. During the present studies, Western blot analyses of bovine 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 body and sclera, but absent in lens. These novel GST isozymes of bovine ocular tissues were purified by immunoaffinity chromatography using the antibodies against rec-mGSTA4-4 and were designated as bGST 5.8 (their 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 degree of primary structure homologies with the corresponding regions of mGSTA4-4 indicating these bovine GST isozymes were distinct from the alpha. 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 the amino acid sequences of bGST 5.8 of cornea and iris-ciliary body and 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 (four-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 towards fatty acid epoxides suggesting that these isozymes may play an important role in protection mechanism against the endogenous toxicants formed during lipid peroxidation.