Among aerobic prokaryotes, many different terminal oxidase complexes
have been described. Sequence comparison has revealed that the aa3-type
cytochrome
c oxidase and the bo3-type
quinol oxidase
are variations on the same theme: the heme-copper oxidase. A third
member
of this family has recently been recognized: the cbb3-type
cytochrome
c oxidase. Here we give an overview, and report that
nitric oxide (NO) reductase, a bc-type cytochrome involved in
denitrification,
shares important features with these terminal oxidases as well.
Tentative
structural, functional and evolutionary implications are discussed.