Effect of ethoxyformic anhydride on the Rieske iron—sulfur protein of bovine heart ubiquinol: Cytochrome c oxidoreductase

Abstract Treatment of bovine heart ubiquinol-cytochrome c oxidoreductase (complex III, bc 1 complex) with ethoxyformic anhydride (EFA) inhibits electron transfer between cytochromes b and c 1 [Yagi et al., Biochemistry 21 (1982) 4777–4782]. This paper shows that EFA alters the EPR lineshape of the Rieske iron—sulfur cluster in complex III and in the isolated Rieske protein without a significant decrease of spin concentration. The effect of EFA on the Rieske iron—sulfur cluster is competitive with that of Q o site inhibitors, such as stigmatellin, and is completely reversed by hydroxylamine. These results are consistent with the possible ethoxyformylation by EFA of histidine ligands of the Rieske iron—sulfur cluster at the non-iron binding imidazole nitrogens.