The bacterial cytochrome cbb3 oxidases

Cytochrome cbb(3) oxidases are found almost exclusively in Proteobacteria, and represent a distinctive class of proton-pumping respiratory heme-copper oxidases (HCO) that lack many of the key structural features that contribute to the reaction cycle of the intensely studied mitochondrial cytochrome c oxidase (CcO). Expression of cytochrome cbb(3) oxidase allows human pathogens to colonise anoxic tissues and agronomically important diazotrophs to sustain N-2 fixation. We review recent progress in the biochemical characterisation of these distinctive oxidases that lays the foundation for understanding the basis of their proposed high affinity for oxygen, ail apparent degeneracy ill their electron input pathways and whether or not they acquired the ability to pump protons independently of other HCOs. (C) 2004 Elsevier B.V. All rights reserved.