title: Function of the iron-sulfur protein of the cytochrome b-c1 segment in electron transfer reactions of the mitochondrial respiratory chain.
abstract: Resolution and reconstitution has been used to examine the involvement of the iron-sulfur protein of the cytochrome b-c1 segment in electron transfer reactions in this region of the mitochondrial respiratory chain. The iron-sulfur protein is required for electron transfer from succinate and from ubiquinol to cytochrome c1. It is not required for reduction of cytochrome b under these conditions, but it is required for oxidation of cytochrome b by cytochrome c plus cytochrome c oxidase. Removal of the iron-sulfur protein from the b-c1 complex prevents reduction of both cytochromes b and c1 by succinate or ubiquinol if antimycin is added to the depleted complex. As increasing amounts of iron-sulfur protein are reconstituted to the depleted complex, the amounts of cytochromes b and c1 reduced by succinate in the presence of antimycin increase and closely parallel the amounts of ubiquinol-cytochrome c reductase activity restored to the reconstituted complex, measured before addition of antimycin. The function of the iron-sulfur protein in these oxidation-reduction reactions is consistent with a cyclic pathway of electron transfer through the cytochrome b-c1 complex, in which the iron-sulfur protein functions as a ubiquinol-cytochrome c1/ubisemiquinone-cytochrome b oxidoreductase.
mesh_terms: D000818:Animals; D002417:Cattle; D003573:Cytochrome b Group; D003580:Cytochromes / Q000378:metabolism; D004579:Electron Transport; D014450:Electron Transport Complex III; D003576:Electron Transport Complex IV / Q000378:metabolism; D007506:Iron-Sulfur Proteins / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008667:Metalloproteins / Q000378:metabolism*; D008929:Mitochondria, Heart / Q000201:enzymology*; D009097:Multienzyme Complexes / Q000378:metabolism*; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D010084:Oxidation-Reduction; D011808:Quinone Reductases / Q000378:metabolism*; D013053:Spectrophotometry
chemical_list: D003573:Cytochrome b Group; D003580:Cytochromes; D007506:Iron-Sulfur Proteins; D008667:Metalloproteins; D009097:Multienzyme Complexes; D009247:NADH, NADPH Oxidoreductases; D011808:Quinone Reductases; D003576:Electron Transport Complex IV; D014450:Electron Transport Complex III