EFFECT OF ETHOXYFORMIC ANHYDRIDE ON THE RIESKE IRON-SULFUR PROTEIN OFBOVINE HEART UBIQUINOL - CYTOCHROME-C OXIDOREDUCTASE

Treatment of bovine heart ubiquinol-cytochrome c oxidoreductase (compl ex III, bc(1) complex) with ethocyformic anhydride (EFA) inhibits elec tron transfer between cytochromes b and c(1) [Yagi et al., Biochemistr y 21 (1982) 4777-4782]. This paper shows that EFA alters the EPR lines hape of the Rieske iron-sulfur cluster in complex III and in the isola ted Rieske protein without a significant decrease of spill concentrati on. The effect of EFA on the Rieske iron-sulfur cluster is competitive with that of Q(0) site inhibitors, such as stigmatellin, and is compl etely 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.