Cytochrome c oxidase (heme aa3) from Paracoccus denitrificans: analysis of mutations in putative proton channels of subunit I.

One of the challenging features of energy-transducing terminal oxidases, like the aa3 cytochrome c oxidase of Paracoccus denitrificans, is the translocation of protons across the cytoplasmic membrane, which is coupled to the transfer of electrons to oxygen. As a prerequisite for a more advanced examination of the enzymatic properties, several amino acid residues, selected on the basis of recent three-dimensional structure determinations, were exchanged in subunit I of the Paracoccus enzyme by site-directed mutagenesis. The properties of the mutated oxidases were analyzed by different methods to elucidate whether they are involved in the coupled and coordinated transfer of protons via two different pathways either to the site of oxygen reduction or through the enzyme from the cytoplasm to the periplasmic side.