title: Kinetic evidence for the re-definition of electron transfer pathways from cytochrome c to O2 within cytochrome oxidase.
abstract: The reaction with O2 of equimolar mixtures of cytochrome c and cytochrome c oxidase in high and low ionic strength buffers has been examined by flow-flash spectrophotometry at room temperature. In low ionic strength media where cytochrome c and the oxidase are bound in an electrostatic, 1:1 complex some of the cytochrome c is oxidised at a faster rate than a metal centre of the oxidase. In contrast, when cytochrome c and cytochrome c oxidase are predominantly dissociated at high ionic strength cytochrome c oxidation occurs only slowly (t1/2 = 5 s) following the complete oxidation of the oxidase. These results demonstrate that maximal rates of electron transfer from cytochrome c to O2 occur when both substrates are present on the enzyme. The heterogeneous oxidation of cytochrome c observed in the complex implies more than one route for electron transfer within the enzyme. Possibilities for new electron transfer pathways from cytochrome c to O2 are proposed.
mesh_terms: D000818:Animals; D002417:Cattle; D003574:Cytochrome c Group / Q000378:metabolism*; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000378:metabolism*; D006736:Horses; D007700:Kinetics; D009206:Myocardium / Q000201:enzymology*; D010084:Oxidation-Reduction; D010101:Oxygen Consumption
chemical_list: D003574:Cytochrome c Group; D003576:Electron Transport Complex IV