title: Effect of ubiquinone extraction on the reaction of the mitochondrial bc1 complex with ferricyanide.
abstract: Depletion of endogenous ubiquinone by pentane extraction of mitochondrial membranes lowered succinate-ferricyanide reductase activity, whereas quinone reincorporation restored the enzymatic activity as well as antimycin sensitivity. The oxidant-induced cytochrome b extrareduction, normally found upon ferricyanide pulse in intact mitochondria in the presence of antimycin, was lost in ubiquinone-depleted membranes, even if cytochrome c was added. Readdition of ubiquinone-2 restored the oxidant-induced extrareduction with an apparent half saturation at 1 mol/mol bc1 complex saturating at about 5 mol/mol. These findings demonstrate a requirement for the ubiquinone pool of the cytochrome b extrareduction. Since the initial rates of cytochrome b reoxidation upon ferricyanide addition, in the presence of antimycin, did not saturate by any ferricyanide concentration in ubiquinone-depleted mitochondria, a direct chemical reaction between ferricyanide and reduced cytochrome b was postulated. The fact that such direct reaction is much faster in ubiquinone-depleted mitochondria may explain the lower antimycin sensitivity of the succinate ferricyanide reductase activity after removal of endogenous ubiquinone.
mesh_terms: D000818:Animals; D002417:Cattle; D004347:Drug Interactions; D014450:Electron Transport Complex III; D005292:Ferricyanides / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D008929:Mitochondria, Heart / Q000201:enzymology*; D009097:Multienzyme Complexes / Q000378:metabolism*; D010084:Oxidation-Reduction; D011808:Quinone Reductases / Q000378:metabolism*; D013054:Spectrophotometry, Atomic; D014451:Ubiquinone / Q000378:metabolism*
chemical_list: D005292:Ferricyanides; D009097:Multienzyme Complexes; D014451:Ubiquinone; C007931:hexacyanoferrate III; D011808:Quinone Reductases; D014450:Electron Transport Complex III