Inhibition of bovine lens glutathione S-transferases by hematin, bilirubin, and bromosulfophthalein.

In order to investigate the binding affinities of ocular lens glutathione S-transferases for non-substrate ligands we have studied the inhibition of bovine lens GSTs by physiological ligands, hematin, bilirubin and the xenobiotic bromosulfophthalein. Hematin was found to be a strong inhibitor as compared to bromosulfophthalein and bilirubin for the two lens isoenzymes, GST 7.4 and GST 5.6, both of which belong to the mu class of GSTs. Except for the competitive inhibition of GST 5.6 by hematin both the isoenzymes were inhibited non-competitively by these compounds. These results indicate binding of these non-substrate ligands to lens GSTs and suggest that similar to the extra ocular GST, the lens GSTs also play a role in the detoxification of hydrophobic compounds through non-catalytic binding.