title: Control of ubiquinol oxidation at center P (Qo) of the cytochrome bc1 complex.
abstract: The unique bifurcated oxidation of ubiquinol at center P (Qo) of the cytochrome bc1 complex is the reaction within the Q-cycle reaction scheme that is most critical for the link between electron transfer and vectorial proton translocation. While there is a general consensus about the overall reaction at center P, the nature of the intermediates and the way the reaction is controlled to ensure obligatory bifurcation is still controversial. By reducing the reaction to its essential steps, a kinetic net rate model is developed in which the activation barrier is associated with the deprotonation of ubiquinol, but the steady state rate is kinetically controlled by the occupancy of the ubiquinol anion and the semiquinone state. This concept is used to interpret experimental data and is discussed in terms of various mechanistic models that are under discussion. It is outlined how other aspects of the center P mechanism like the proposed "prosthetic" ubiquinone and the moving domain of the "Rieske" protein could be incorporated in the kinetic framework.
authors.affiliation: Universitätsklinikum Frankfurt, Institut für Biochemie I, Zentrum der Biologischen Chemie, Frankfurt am Main, Federal Republic of Germany. brandt@zbc.klinik.uni-frankfurt.de
authors.forename: U
authors.initials: U
authors.lastname: Brandt
mesh_terms: D000818:Animals; D004579:Electron Transport; D014450:Electron Transport Complex III / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006418:Heme / Q000737:chemistry; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology; D008956:Models, Chemical; D008958:Models, Molecular; D009038:Motion; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011522:Protons; D013267:Stilbenes / Q000494:pharmacology; D013329:Structure-Activity Relationship; D013816:Thermodynamics; D014451:Ubiquinone / Q000031:analogs & derivatives* / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D007506:Iron-Sulfur Proteins; D011522:Protons; C037989:Rieske iron-sulfur protein; D013267:Stilbenes; C056108:3-methoxy-2-(2-styrylphenyl)propenic acid methyl ester; D014451:Ubiquinone; D006418:Heme; D014450:Electron Transport Complex III; C003741:ubiquinol