Modulation of the electron-proton coupling at cytochrome a by the ligation of the oxidized catalytic center in bovine cytochrome c oxidase.

Cytochrome a was suggested as the key redox center in the proton pumping process of bovine cytochrome c oxidase (CcO). Recent studies showed that both the structure of heme a and its immediate vicinity are sensitive to the ligation and the redox state of the distant catalytic center composed of iron of cytochrome a (Fe) and copper (Cu). Here, the influence of the ligation at the oxidized Fe-Cu center on the electron-proton coupling at heme a was examined in the wide pH range (6.

Response of Heme Symmetry to the Redox State of Bovine Cytochrome c Oxidase.

Second-derivative absorption spectroscopy was employed to monitor the response of effective symmetry of cytochromes a and a to the redox and ligation states of bovine cytochrome c oxidase (CcO). The Soret band π → π* electronic transitions were used to display the changes in symmetry of these chromophores induced by the reduction of CcO inhibited by the exogenous ligands and during catalytic turnover. The second derivative of the difference absorption spectra revealed only a single Soret band for the oxidized cytochromes a and a and cyanide-ligated oxidized cytochrome a.