Redox Bohr effects and the role of heme a in the proton pump of bovine heart cytochrome c oxidase

Structural and functional observations are reviewed which provide evidence for a central role of redox Bohr effect linked to the low-spin heme a in the proton pump of bovine heart cytochrome c oxidase. Data on the membrane sidedness of Bohr protons linked to anaerobic oxido-reduction of the individual metal centers in the liposome reconstituted oxidase are analysed. Redox Bohr protons coupled to anaerobic oxido-reduction of heme a (and CuA) and CuB exhibit membrane vectoriality, i.e. protons are taken up from the inner space upon reduction of these centers and released in the outer space upon their oxidation. Redox Bohr protons coupled to anaerobic oxido-reduction of heme a3 do not, on the contrary, exhibit vectorial nature: protons are exchanged only with the outer space. A model of the proton pump of the oxidase, in which redox Bohr protons linked to the low-spin heme a play a central role, is described. This article is part of a Special Issue entitled: Allosteric cooperativity in respiratory proteins