Coupling of Proton Transfer to Oxygen Chemistry in Cytochrome Oxidase: the Roles of Residues I67 and E243

Summary

We are studying mutant forms of cytochrome oxidase to investigate residues of importance for proton movement and for sites of redox-linked protonation. In this chapter, we describe the effects of a mutation in the residue I67. The mutation alters the redox properties of heure a, probably by perturbing the pK of E243, a conserved residue that we propose to be a protonation site that is redox-linked to heme a This mutation has little effect on the other redox centers or on the ligand reactions of the binuclear center. The effects are compared with those of the mutation K362M, a change that has no effect on the redox properties of heure a but instead alters the reducibility of the binuclear center, probably by preventing protonations that are required for more than one charge to be accumulated on the heure a ₃/Cu_Bsystem.