Modification of the Mitochondrial Sulfonylurea Receptor by Thiol Reagents

The purpose of this study was to investigate the effects exerted by thiol-modifying reagents on themitochondrial sulfonylurea receptor. The thiol-oxidizing agents (timerosal and 5,5′-dithio-bis(2-nitrobenzoic acid)) were found to produce a large inhibition (70% to 80%) of specific binding of [3H]glibenclamide to the beef heart mitochondrial membrane. Similar effects were observed with membrane permeable (N-ethylmaleimide) and non-permeable (mersalyl) thiol modifying agents. Glibenclamide binding was also decreased by oxidizing agents (hydrogen peroxide) but not by reducing agents (reduced gluthatione, dithiothreitol and the 2,3-dihydroxy-1,4-dithiolbutane). The results suggest that intact thiol groups, facing the mitochondrial matrix, are essential for glibenclamide binding to the mitochondrial sulfonylurea receptor.