The rate-limiting step and nonhyperbolic kinetics in the oxidation of ferrocytochrome c catalyzed by cytochrome c oxidase.
The level of reduction of cytochrome a and CuA during the oxidation of ferrocytochrome c has been determined in stopped-flow experiments. Both components are partially reduced but become progressively more oxidized as the reaction proceeds. When all cytochrome c has been oxidized, CuA is also completely oxidized, whereas cytochrome a is still partially reduced. These results can be simulated on the basis of a model which requires that the intramolecular electron transfer from cytochrome a and CuA to cytochrome a3-CuB is a two-electron process and, in addition, that the binding of oxidized cytochrome c to the electron- transfer site decreases the rate constants for intramolecular electron transfer from cytochrome a. The first requirement is related to the function of the oxidase as a proton pump. Product dissociation is not by itself rate-limiting, making it less likely that the source of the nonhyperbolic substrate kinetics is an effect on this step from electrostatic interaction with ferricytochrome c bound to a second site. It is pointed out that nonhyperbolic kinetics is, in fact, an intrinsic property of ion pumps.
D000818:Animals; D002384:Catalysis; D002417:Cattle; D003573:Cytochrome b Group / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism*; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000378:metabolism*; D007700:Kinetics; D010084:Oxidation-Reduction
D003573:Cytochrome b Group; D003574:Cytochrome c Group; D003576:Electron Transport Complex IV