cytochromes-c1 and duroquinol

The reduction of cyctochromes c + c1 by durohydroquinone and ferrocyanide in electron transport particles (ETP) and intact cytochrome c-depleted beef heart mitochondria has been studied. At least 94% of the ETP are in an inverted orientation. Durohydroquinone reduces 80% of c + c1 in ETP but less than 20% in mitochondria; sonication of mitochondria allows reduction of cytochromes c + c1 (80%). Addition of ferrocyanide (effective redox potential +245 mV) to electron transport particles results in 30% reduction of cytochromes c + c1. Addition of ferrocyanide to intact cytochrome c-depleted mitochondria does not reduce cytochrome c1; treatment with N,N,N',N'-tetramethylphenylenediamine, Triton X-100, or sonic oscillation results in 30% reduction of cytochromes c + c1. The Km value of ferrocyanide oxidase for K-ferrocyanide is pH-dependent in ETP only, increasing with increasing pH. The extent of reduction of cytochrome c1 is also pH-dependent in ETP only, the extent of reduction increasing with decreasing pH. On the basis of these data cytochrome c1 is exposed to the matrix face and cytochrome c is exposed to the cytoplasmic face. No redox center other than cytochrome c in the segment between the antimycin site and cytochrome c is exposed on the C-side.

Topics: Animals; Cattle; Cytochrome c Group; Cytochromes c1; Electron Transport; Electron Transport Complex III; Ferrocyanides; Hydroquinones; Kinetics; Mitochondria, Heart; Multienzyme Complexes; NADH, NADPH Oxidoreductases; Oxidation-Reduction; Quinone Reductases; Submitochondrial Particles

The triphasic course previously reported for the reduction of cytochrome b in the succinate-cytochrome c reductase by either succinate or duroquinol has been shown to be dependent on the redox state of the enzyme preparation. Prior reduction with increasing concentrations of ascorbate leads to partial reduction of cytochrome c1, and a gradual decrease in the magnitude of the oxidation phase of cytochrome b. At an ascorbate concentration sufficient to reduce cytochrome c1 almost completely, the reduction of cytochrome b by either succinate or duroquinol becomes monophasic. Owing to the presence of a trace amount of cytochrome oxidase in the reductase preparation employed, the addition of cytochrome c makes electron flow from substrate to oxygen possible. Under such circumstances, the addition of a limited amount of either succinate or duroquinol leads to a multiphasic reduction and oxidation of cytochrome b. After the initial three phases as described previously, cytochrome b becomes oxidized before cytochrome c1 when the limited amount of added substrate is being used up. However, at the end of the reaction when cytochrome c1 is being rapidly oxidized, cytochrome b becomes again reduced. The above observations support a cyclic scheme of electron flow in which the reduction of cytochrome b proceeds by two different routes and its oxidation controlled by the redox state of a component of the respiratory chain.

Topics: Animals; Antimycin A; Ascorbic Acid; Cytochrome b Group; Cytochromes c1; Hydroquinones; Kinetics; Oxidation-Reduction; Oxidoreductases; Succinate Cytochrome c Oxidoreductase