title: The mechanism of proton translocation by the cytochrome system of mitochondria. Characterization of proton-transfer reactions associated with oxidoreductions of terminal respiratory carriers.
abstract: A direct kinetic analysis is presented of rapid proton-releasing reactions at the outer or C-side of the membrane, in ox heart and rat liver mitochondria, associated with aerobic oxidation of reduced terminal respiratory carriers in the presence of antimycin. Valinomycin plus K+ enhances the rate of cytochrome c oxidation and the rate and extent of H+ release. In the presence of valinomycin the leads to H+/e- ratio, computed on the basis of total electron flow from respiratory carriers to oxygen, varies with pH, remaining always lower than 1, and is unaffected by N-ethylmaleimide. 2-Heptyl-4-hydroxyquinoline N-oxide and 5-(n-undecyl)-6-hydroxy-4,7-dioxobenzothiazole, at concentrations which inhibit in the presence of antimycin the oxygen-induced reduction of b cytochromes, cause also a marked depression of the H+ release associated with aerobic oxidation of terminal respiratory carriers. Aerobic oxidation of the cytochrome system in mitochondria and of isolated b-c1 complex and cytochrome c oxidase results in scalar proton release from ionizable groups (redox Bohr effects). In mitochondria and submitochondrial particles, about 70% of the oxidoreductions of the components of the cytochrome system are linked to scalar proton transfer by ionizable groups. In isolated b-c1 complex scalar proton transfer, resulting from redox Bohr effect, amounts to 0.9H+ per Fe-S protein (190 muT). In isolated cytochrome c oxidase, Bohr protons amount to 0.8 per haem a + a3. The results presented indicate that the H+ release from mitochondria during oxidation of terminal respiratory carriers derives from residual antimycin-insensitive electron flow in the quinone-cytochrome c span and from redox Bohr effects in the b-c1 complex and cytochrome c oxidase. There is no sign of proton pumping by cytochrome oxidase during its transition from the reduced to the active 'pulsed' state and the first one or two turnovers.
mesh_terms: D000818:Animals; D002417:Cattle; D003580:Cytochromes / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D006912:Hydroxyquinolines / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008929:Mitochondria, Heart / Q000187:drug effects / Q000201:enzymology*; D008930:Mitochondria, Liver / Q000187:drug effects / Q000201:enzymology*; D010084:Oxidation-Reduction; D011522:Protons; D051381:Rats; D013844:Thiazoles / Q000494:pharmacology; D014634:Valinomycin / Q000494:pharmacology
chemical_list: C025993:5-n-undecyl-6-hydroxy-4,7-dioxobenzothiazole; D003580:Cytochromes; D006912:Hydroxyquinolines; D011522:Protons; D013844:Thiazoles; C001333:2-(n-heptyl)-4-hydroxyquinoline N-oxide; D014634:Valinomycin