This family consists of cytochrome bd type terminal oxidases that catalyse quinol-dependent, Na+-independent oxygen uptake [2]. Members of this family are integral membrane proteins and contain a protohaem IX centre B558. One member of the family Swiss:O05192 is implicated in having an important role in micro-aerobic nitrogen fixation in the enteric bacterium Klebsiella pneumoniae [1]. The family forms an integral functional unit with subunit I, family Bac_Ubq_Cox, Pfam:PF01654.

1: The Klebsiella pneumoniae cytochrome bd' terminal oxidase complex and its role in microaerobic nitrogen fixation. Juty NS, Moshiri F, Merrick M, Anthony C, Hill S; Microbiology 1997;143:2673-2683. PMID:9274021

2: Purification of a cytochrome bd terminal oxidase encoded by the Escherichia coli app locus from a delta cyo delta cyd strain complemented by genes from Bacillus firmus OF4. Sturr MG, Krulwich TA, Hicks DB; J Bacteriol 1996;178:1742-1749. PMID:8626304