Soluble cytochrome b-c1 complex and the reconstitution of succinate-cytochrome c reductase.

The cytochrome b-c1 complex has been “solubilized” and purified to a stage containing 6.5 nmoles of cytochrome b per mg of protein. Seven bands are resolved on a polyacrylamide gel electrophoretic column in sodium dodecyl sulfateP-mercaptoethanol medium. Five of these seven bands have been identified as cytochromes b and cl and a non-heme iron protein. The remaining two bands might be associated with these components or, less likely, might be impurities but do not belong to the so-called structural proteins. The cytochrome b-n complex is enzymatically active and can reconstitute with soluble succinate dehydrogenase to form an integral entity of antimycin A-sensitive succinate-cytochrome c reductase. The reconstituted reductase shows the same structural and functional characteristics as the intact reductase. The total number of the p-hydroxymercuribenzoate (p-MB) titratable groups in the cytochrome b-cl complex has been found to be 11 f 1 moles per mole of cytochrome b. The p-MB-reacted complex is inactive in reconstitution but shows the same catalytic activity in the oxidation of reduced ubiquinone by cytochrome c.