title: Studies on the succinate dehydrogenating system. Isolation and properties of the mitochondrial succinate-ubiquinone reductase.
abstract: A simple procedure for preparation of highly purified soluble succinate-ubiquinone reductase from bovine heart mitochondrial particles is described. The enzyme exhibits four major bands on sodium dodecyl sulfate gel electrophoresis and contains (nmol per mg protein): covalently bound flavin, 6; non-heme iron, 53; acid-labile sulfur, 50; cytochrome b-560 heme, 1.2. The enzyme catalyzes thenoyltrifluoroacetone, or carboxin-sensitive (pure non-competitive with Q2) reduction of Q2 by succinate with a turnover number close to that in parent submitochondrial particles. The succinate reduced enzyme exhibits ferredoxin-type iron-sulfur center EPR-signal (g = 1.94 species) and a semiquinone signal (g = 2.00). An oxidized preparation shows a symmetric signal centered around g = 2.01. An unusual dissociation of the enzyme in the absence of a detergent is described. When added to the assay mixture from a concentrated protein-detergent solution, the enzyme does not reduce Q2 being highly reactive towards ferricyanide ('low Km ferricyanide reactive site'; Vinogradov, A.D., Gavrikova, E.V. and Goloveshkina, V.G. (1975) Biochem. Biophys. Res. Commun. 65, 1264-1269). The ubiquinone reductase, not the ferricyanide reductase was observed when the enzyme was added to the assay mixture from the diluted protein-detergent solutions. Thus the dissociation of succinate dehydrogenase from the complex occurs in the absence of a detergent dependent on the concentration of the protein-detergent complex in the stock preparation where the samples for the assay are taken from. An active antimycin-sensitive succinate-cytochrome c reductase was reconstituted by admixing of the soluble succinate-ubiquinone reductase and the cytochrome b-c1 complex, i.e., from the complexes which both contain the ubiquinone reactivity conferring protein (QPs). Cytochrome c reductase was also reconstituted from the succinate-ubiquinone reductase and succinate-cytochrome c reductase containing inactivated succinate dehydrogenase. The reconstitution experiments suggest that there exists a specific protein-protein (or lipid) interaction between QPs and a certain component(s) of the b-c1 complex.
mesh_terms: D000818:Animals; D001665:Binding Sites; D002417:Cattle; D004578:Electron Spin Resonance Spectroscopy; D042963:Electron Transport Complex II; D004591:Electrophoresis, Polyacrylamide Gel; D005415:Flavins / Q000032:analysis; D006418:Heme / Q000032:analysis; D007501:Iron / Q000032:analysis; D007700:Kinetics; D008929:Mitochondria, Heart / Q000201:enzymology*; D009097:Multienzyme Complexes / Q000302:isolation & purification / Q000378:metabolism*; D017830:Octoxynol; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000302:isolation & purification / Q000378:metabolism*; D011092:Polyethylene Glycols / Q000494:pharmacology; D013053:Spectrophotometry; D013379:Substrate Specificity; D013385:Succinate Dehydrogenase / Q000302:isolation & purification / Q000378:metabolism*; D013386:Succinates / Q000378:metabolism; D019802:Succinic Acid; D013455:Sulfur / Q000032:analysis; D014451:Ubiquinone / Q000032:analysis / Q000378:metabolism
chemical_list: D005415:Flavins; D009097:Multienzyme Complexes; D013386:Succinates; D014451:Ubiquinone; D011092:Polyethylene Glycols; D006418:Heme; D013455:Sulfur; D017830:Octoxynol; D019802:Succinic Acid; D007501:Iron; D010088:Oxidoreductases; D042963:Electron Transport Complex II; D013385:Succinate Dehydrogenase; C025204:Ubiquinone Q2