The rate-limiting step and nonhyperbolic kinetics in the oxidation of ferrocytochrome c catalyzed by cytochrome c oxidase

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Abstract

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. © 1986.

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Brzezinski, P., Thörnström, P. E., & G. Malmström, B. (1986). The rate-limiting step and nonhyperbolic kinetics in the oxidation of ferrocytochrome c catalyzed by cytochrome c oxidase. FEBS Letters, 194(1), 1–5. https://doi.org/10.1016/0014-5793(86)80040-0

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