title: A new species of bound ubisemiquinone anion in QH2: cytochrome c oxidoreductase.
abstract: Using a combination of EPR and low temperature diffuse reflectance spectroscopy, a new species of semiquinone anion has been detected in QH2:cytochrome c oxidoreductase in submitochondrial particles under conditions of oxidant-induced extra reduction of cytochrome b. In contrast to the previously detected semiquinone anion, this new species is insensitive to antimycin but sensitive to treatment with 2,3-dimercaptopropanol and O2. The two species can easily be distinguished on the basis of their respective EPR properties since they differ in g-value, line width, and microwave power saturation behavior. It is concluded that the two species of semiquinone anion are bound to different domains on QH2:cytochrome c oxidoreductase. The existence of two different semiquinone anions in the enzyme strongly supports a mechanism of electron flow as proposed in the Q-cycle.
mesh_terms: D000818:Animals; D002417:Cattle; D003067:Coenzymes; D003574:Cytochrome c Group / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D014450:Electron Transport Complex III; D007700:Kinetics; D008928:Mitochondria / Q000201:enzymology*; D008929:Mitochondria, Heart / Q000201:enzymology*; D009097:Multienzyme Complexes / Q000378:metabolism*; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D011485:Protein Binding; D011808:Quinone Reductases / Q000378:metabolism*; D013367:Submitochondrial Particles / Q000201:enzymology*; D014451:Ubiquinone / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D003067:Coenzymes; D003574:Cytochrome c Group; D009097:Multienzyme Complexes; D014451:Ubiquinone; D009247:NADH, NADPH Oxidoreductases; D011808:Quinone Reductases; D014450:Electron Transport Complex III; C024989:coenzyme Q10