Kinetic Coupling Between Electron and Proton Transfer in Cytochrome C Oxidase: Simultaneous Measurements of Conductance and Absorbance Changes

Overview

Journal Proc Natl Acad Sci U S A

Specialty Science

Date 1996 Oct 29

PMID 8901574

Citations 8

Authors

P Adelroth

H Sigurdson

S Hallen

P Brzezinski

Affiliations

Soon will be listed here.

Abstract

Bovine heart cytochrome c oxidase is an electron-current driven proton pump. To investigate the mechanism by which this pump operates it is important to study individual electron- and proton-transfer reactions in the enzyme, and key reactions in which they are kinetically and thermodynamically coupled. In this work, we have simultaneously measured absorbance changes associated with electron-transfer reactions and conductance changes associated with protonation reactions following pulsed illumination of the photolabile complex of partly reduced bovine cytochrome c oxidase and carbon monoxide. Following CO dissociation, several kinetic phases in the absorbance changes were observed with time constants ranging from approximately 3 microseconds to several milliseconds, reflecting internal electron-transfer reactions within the enzyme. The data show that the rate of one of these electron-transfer reactions, from cytochrome a3 to a on a millisecond time scale, is controlled by a proton-transfer reaction. These results are discussed in terms of a model in which cytochrome a3 interacts electrostatically with a protonatable group, L, in the vicinity of the binuclear center, in equilibrium with the bulk through a proton-conducting pathway, which determines the rate of proton transfer (and indirectly also of electron transfer). The interaction energy of cytochrome a3 with L was determined independently from the pH dependence of the extent of the millisecond-electron transfer and the number of protons released, as determined from the conductance measurements. The magnitude of the interaction energy, 70 meV (1 eV = 1.602 x 10(-19) J), is consistent with a distance of 5-10 A between cytochrome a3 and L. Based on the recently determined high-resolution x-ray structures of bovine and a bacterial cytochrome c oxidase, possible candidates for L and a physiological role for L are discussed.

Citing Articles

Functions of the hydrophilic channels in protonmotive cytochrome c oxidase.

Rich P, Marechal A J R Soc Interface. 2013; 10(86):20130183.

PMID: 23864498 PMC: 3730678. DOI: 10.1098/rsif.2013.0183.

Functional interactions between membrane-bound transporters and membranes.

Ojemyr L, Lee H, Gennis R, Brzezinski P Proc Natl Acad Sci U S A. 2010; 107(36):15763-7.

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Nanosecond electron tunneling between the hemes in cytochrome bo3.

Jasaitis A, Johansson M, Wikstrom M, Vos M, Verkhovsky M Proc Natl Acad Sci U S A. 2007; 104(52):20811-4.

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On the role of the K-proton transfer pathway in cytochrome c oxidase.

Branden M, Sigurdson H, Namslauer A, Gennis R, Adelroth P, Brzezinski P Proc Natl Acad Sci U S A. 2001; 98(9):5013-8.

PMID: 11296255 PMC: 33155. DOI: 10.1073/pnas.081088398.

The proton collecting function of the inner surface of cytochrome c oxidase from Rhodobacter sphaeroides.

Marantz Y, Nachliel E, Aagaard A, Brzezinski P, Gutman M Proc Natl Acad Sci U S A. 1998; 95(15):8590-5.

PMID: 9671722 PMC: 21120. DOI: 10.1073/pnas.95.15.8590.

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