Functional analogues of cytochrome c oxidase, myoglobin, and hemoglobin.

The majority of modern organisms, including many prokaryotes, are aerobes;1 that is, they use molecular oxygen as the terminal electron acceptor for energy generation. Although nearly every redox gradient in nature appears to be utilized by one organism or another,2-4 aerobic metabolism predominates, in large part due to the highly exergonic nature of the four-electron, four-proton (4e/4H+) reduction of O2 to H2O (reaction 1). A multicellular aerobe requires an