Proton Translocation by Cytochrome c Oxidase Can Take Place without the Conserved Glutamic Acid in Subunit I

A glutamic acid residue in subunit I of the heme−copper oxidases is highly conserved and has been directly implicated in the O2 reduction and proton-pumping mechanisms of these respiratory enzymes. Its mutation to residues other than aspartic acid dramatically inhibits activity, and proton translocation is lost. However, this glutamic acid is replaced by a nonacidic residue in some structurally distant members of the heme−copper oxidases, which have a tyrosine residue in the vicinity. Here, using cytochrome c oxidase from Paracoccus denitrificans, we show that replacement of the glutamic acid and a conserved glycine nearby lowers the catalytic activity to