title: Purification of a reconstitutively active iron-sulfur protein (oxidation factor) from succinate . cytochrome c reductase complex of bovine heart mitochondria.
abstract: Oxidation factor, a protein required for electron transfer from succinate to cytochrome c in the mitochondrial respiratory chain, has been purified from isolated succinate . cytochrome c reductase complex. Purification of the protein has been followed by a reconstitution assay in which restoration of ubiquinol . cytochrome c reductase activity is proportional to the amount of oxidation factor added back to depleted reductase complex. The purified protein is a homogeneous polypeptide on acrylamide gel electrophoresis in sodium dodecyl sulfate and migrates with an apparent Mr = 24,500. Purified oxidation factor restores succinate . cytochrome c reductase and ubiquinol . cytochrome c reductase activities to depleted reductase complex. It is not required for succinate dehydrogenase nor for succinate . ubiquinone reductase activities of the reconstituted reductase complex. Oxidation factor co-electrophoreses with the iron-sulfur protein polypeptide of ubiquinol . cytochrome c reductase complex. The purified protein contains 56 nmol of nonheme iron and 36 nmol of acid-labile sulfide/mg of protein and possesses an EPR spectrum with the characteristic "g = 1.90" signal identical to that of the iron-sulfur protein of the cytochrome b . c1 complex. In addition, the optimal conditions for extraction of oxidation factor, including reduction with hydrosulfite and treatment of the b . c1 complex with antimycin, are identical to those which facilitate extraction of the iron-sulfur protein from the b . c1 complex. These results indicate that oxidation factor is a reconstitutively active form of the iron-sulfur protein of the cytochrome b . c1 complex first discovered by Rieske and co-workers (Rieske, J.S., Maclennan, D.H., and Coleman, R. (1964) Biochem. Biophys. Res. Commun. 15, 338-344) and thus demonstrate that this iron-sulfur protein is required for electron transfer from ubiquinol to cytochrome c in the mitochondrial respiratory chain.
mesh_terms: D000818:Animals; D002417:Cattle; D004578:Electron Spin Resonance Spectroscopy; D007506:Iron-Sulfur Proteins / Q000302:isolation & purification* / Q000378:metabolism; D007700:Kinetics; D008667:Metalloproteins / Q000302:isolation & purification*; D008929:Mitochondria, Heart / Q000201:enzymology*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000302:isolation & purification*; D013384:Succinate Cytochrome c Oxidoreductase / Q000302:isolation & purification* / Q000378:metabolism; D014357:Trypsin / Q000494:pharmacology
chemical_list: D007506:Iron-Sulfur Proteins; D008667:Metalloproteins; D010088:Oxidoreductases; D013384:Succinate Cytochrome c Oxidoreductase; D014357:Trypsin