Cytochrome c oxidase in Paracoccus denitrificans. Protein, chemical, structural, and evolutionary aspects

Preparations and protein chemical characterizations performed with cytochrome c oxidase (E.C. 1.9.3.1) from the purple bacterium Paracoccus denitrificans are reviewed. The simplest catalytically competent complex of the enzyme consists of two subunits of 62012 and 2799 Da. The theoretical heme a/protein ratio of the purified enzyme is 22.0 nmol/mg. The amino acid sequences of both proteins are compared with examples of subunits I and II of mitochondrial terminal oxidases from the main kingdoms of eukaryotes. The significance of the emerging conserved features such as membrane penetration patterns, invariant residues, stoichiometry, and sites of prosthetic groups are discussed. The Paracoccus enzyme represents the only prokaryotic oxidase detailed so far, which is directly related to the mitochondrial oxidases by common ancestry in the growing O2 atmosphere.