Localization of a ferricyanide-reactive site of cytochrome b-c1 complex, possibly of cytochrome b or ubisemiquinone, at the outer face of submitochondrial particles

When succinate oxidation by submitochondrial particles is blocked by antimycin, NoHOQnO or funiculosin, addition of ferricyanide restores oxygen uptake coupled to membrane potential generation. The effect of ferricyanide is abolished by mucidin or myxothiazol, as well as by KCN. The data strongly favor a cyclic redox loop mechanism in site 2 and show that either heme of the ferrous cytochrome b or ubisemiquinone formed in the QH2-oxidizing center of complex b−c1 is accessible to ferricyanide at the outer (M) side of the submitochondrial particle membrane.