Proton translocation in cytochrome c oxidase: Redox linkage through proximal ligand exchange on cytochrome a3

Denis L. Rousseau, Yuan chin Ching, Jianling Wang

Research output: Contribution to journalArticlepeer-review

55 Scopus citations


An analysis of resonance Raman scattering data from CO-bound cytochrome c oxidase and from the photodissociated enzyme indicates that histidine may not be coordinated to the iron atom of cytochrome a3 in the CO-bound form of the enzyme. Instead, the data suggest that either a water molecule or a different amino acid residue occupies the proximal ligand position. From these data, it is postulated that ligand exchange on cytochrome a3 can occur under physiological conditions. Studies of mutant hemoglobins have demonstrated that tyrosinate binds preferentially to histidine in the ferric forms of the proteins. In cytochrome c oxidase tyrosine residues are located near the histidine residues recently implicated in coordination to cytochrome a3 (Shapleigh et al., 1992; Hosler et al., this volume). Expanding on these concepts, we propose a model for proton translocation at the O2-binding site based on proximal ligand exchange between tyrosine and histidine on cytochrome a3. The pumping steps take place at the level of the peroxy intermediate and at the level of the ferryl intermediate in the catalytic cycle and are thereby consistent with the recent results of Wilkstrom (1989) who found that proton pumping occurs only at these two steps. It is shown that the model may be readily extended to account for the pumping of two protons at each of the steps.

Original languageEnglish (US)
Pages (from-to)165-176
Number of pages12
JournalJournal of Bioenergetics and Biomembranes
Issue number2
StatePublished - Apr 1993
Externally publishedYes


  • Proton pumping
  • Raman scattering
  • electron transfer
  • heme proteins
  • proton translocation

ASJC Scopus subject areas

  • Physiology
  • Cell Biology


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