Cytochrome c oxidase: understanding nature's design of a proton pump

It has been estimated that nearly 90% of the O_2 consumed aerobic organisms participates in the dioxygen chemistry cytochrome c oxidase and becomes reduced to water in the step of respiration. Cytochrome oxidases of the aa_3 (having two a-type cytochromes) are found in a wide of aerobic organisms including bacteria, fungi, single- eukaryotes, plants, and animals. It is an integral protein complex comprised of 2 or 3 subunits in simplest bacterial systems and as many as 13 dissimilar in mammals [for a review, see Wikström et al. (1981)].