Figure 1.

Branched respiratory chain of P. aeruginosa. Under aerobic conditions, oxygen is utilized as a terminal electron acceptor and reduced to water by five terminal oxidases. Two quinol oxidases, the bo₃ oxidase and the cyanide-insensitive oxidase, receive electrons directly from quinol. Three cytochrome c oxidases, the aa₃ oxidase and the two cbb₃ oxidases, receive electrons via the cytochrome bc₁ complex and c-type cytochromes or a small blue-copper protein azurin. Under anaerobic conditions, electrons are transferred to nitrogen oxides via the denitrification enzymes.