Protonmotive cooperativity in cytochrome c oxidase

Cooperative linkage of solute binding at separate binding sites in allosteric proteins is an important functional attribute of soluble and membrane bound hemoproteins. Analysis of proton/electron coupling at the four redox centers, i.e. CuA, heme a, heme a3 and CuB, in the purified bovine cytochrome c oxidase in the unliganded, CO-liganded and CN-liganded states is presented. These studies are based on direct measurement of scalar proton translocation associated with oxido-reduction of the metal centers and pH dependence of the midpoint potential of the redox centers. Heme a (and CuA) exhibits a cooperative proton/electron linkage (Bohr effect). Bohr effect seems also to be associated with the oxygenreduction chemistry at the heme a3–CuB binuclear center. Data on electron transfer in cytochrome c oxidase are also presented, which, together with structural data, provide evidence showing the occurrence of direct electron transfer from CuA to the binuclear center in addition to electron transfer via heme a. A survey of structural and functional data showing the essential role of cooperative proton/electron linkage at heme a in the proton pump of cytochrome c oxidase is presented. On the basis of this and related functional and structural information, variants for cooperative mechanisms in the proton pump of the oxidase are examined.