The role of water near cytochrome a in cytochrome c oxidase

Denis L. Rousseau, M. Sassaroli, Y. C. Ching, S. Dasgupta

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

Resonance Raman scattering studies of cytochrome c oxidase reveal that two vibrational modes narrow upon placing the enzyme in D2O. This is interpreted as evidence for the presence of water molecules near cytochrome a that increase the linewidth of the heme modes due to resonance vibrational energy transfer to the H2O2 bending mode. From the nature of the modes in which the broadening is detected, it is deduced that the water molecules are located near the formyl and the vinyl substituents of the cytochrome a. The change in width in the formyl mode appears quickly, whereas that in the vinyl mode only develops after extended exposure of the enzyme to D2O. On the basis of these results we propose a new mechanism for proton translocation. In this hypothesis water molecules at the active site become activated and are dissociated into protons and hydroxyl groups due to changes in the pK(a)s of residues near the heme when the redox state of the cytochrome a changes. Structural features of the protein stabilize this charge separation and allow directional migration of protons to the cytosolic side of the inner mitochondrial membrane. It is pointed out that this mechanism may be operative in all proton-translocation complexes, and it is observed that in bacteriorhodopsin, also a proton pump, water molecules are detected near the active site lending support to the generality of this mechanism.

Original languageEnglish (US)
Pages (from-to)223-237
Number of pages15
JournalAnnals of the New York Academy of Sciences
Volume550
StatePublished - 1989
Externally publishedYes

Fingerprint

Cytochromes a
Electron Transport Complex IV
Protons
Molecules
Water
Heme
Catalytic Domain
Bacteriorhodopsins
Proton Pumps
Raman Spectrum Analysis
Energy Transfer
Mitochondrial Membranes
Enzymes
Linewidth
Hydroxyl Radical
Energy transfer
Oxidation-Reduction
Raman scattering
Membranes
Proteins

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)

Cite this

The role of water near cytochrome a in cytochrome c oxidase. / Rousseau, Denis L.; Sassaroli, M.; Ching, Y. C.; Dasgupta, S.

In: Annals of the New York Academy of Sciences, Vol. 550, 1989, p. 223-237.

Research output: Contribution to journalArticle

Rousseau, Denis L. ; Sassaroli, M. ; Ching, Y. C. ; Dasgupta, S. / The role of water near cytochrome a in cytochrome c oxidase. In: Annals of the New York Academy of Sciences. 1989 ; Vol. 550. pp. 223-237.
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AU - Ching, Y. C.

AU - Dasgupta, S.

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AB - Resonance Raman scattering studies of cytochrome c oxidase reveal that two vibrational modes narrow upon placing the enzyme in D2O. This is interpreted as evidence for the presence of water molecules near cytochrome a that increase the linewidth of the heme modes due to resonance vibrational energy transfer to the H2O2 bending mode. From the nature of the modes in which the broadening is detected, it is deduced that the water molecules are located near the formyl and the vinyl substituents of the cytochrome a. The change in width in the formyl mode appears quickly, whereas that in the vinyl mode only develops after extended exposure of the enzyme to D2O. On the basis of these results we propose a new mechanism for proton translocation. In this hypothesis water molecules at the active site become activated and are dissociated into protons and hydroxyl groups due to changes in the pK(a)s of residues near the heme when the redox state of the cytochrome a changes. Structural features of the protein stabilize this charge separation and allow directional migration of protons to the cytosolic side of the inner mitochondrial membrane. It is pointed out that this mechanism may be operative in all proton-translocation complexes, and it is observed that in bacteriorhodopsin, also a proton pump, water molecules are detected near the active site lending support to the generality of this mechanism.

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