On the functional role of coupling factor B in the mitochondrial H+ -ATPase

Evidence for the presence of a functionally important vicinal dithiol in mitochondrial coupling factor B (FB) has been presented earlier (Sanadi, D. R. (1982) Biochim. Biophys. Acta 683, 39-56). FB was completely inactivated by 38 micron of copper o-phenanthroline or 0.63 mM iodosobenzoate, and the kinetics were consistent with intramolecular disulfide formation as were polyacrylamide gel patterns which showed that FB which had been treated with copper o-phenanthroline had a different mobility from that of untreated FB. ATP-Pi exchange activity and ATP-induced binding of bis[3-propyl-5-oxoisoxazol-4-yl]pentamethine oxonol (oxonol VI) to H+ -ATPase were also inhibited by the thiol oxidizing reagents, although oligomycin-sensitive ATPase activity was unaffected. F0 isolated from H+ -ATPase rebinds purified F1 with the restoration of ATP-induced oxonol-binding activity. Prior treatment of F0 (but not of F1) with copper o-phenanthroline abolished the oxonol-binding activity of reconstituted F0-F1. 115Cd binds tightly to H+ -ATPase and the bound protein can be recovered by gel electrophoresis in phosphate buffer in the presence of sodium dodecyl sulfate at a position corresponding to FB. Prior treatment of the H+ -ATPase with copper o-phenanthroline abolished 115Cd binding. The results indicate that the major effect of these inhibitors is on FB dithiol and leave little doubt that Cd2+ is indeed bound to a vicinal dithiol group.