7.1.1.5 metabolism the FMN enzyme protoporphyrinogen IX oxidase (HemG) of Escherichia coli abstracts six electrons from its substrate and transfers them via ubiquinone, cytochrome bo3 and cytochrome bd oxidase to oxygen. Under anaerobic conditions electrons are transferred via menaquinone, fumarate and nitrate reductase. Cyo, Cyd and Nar contribute to the proton motive force that drives ATP formation. oxygen-dependent cytochrome oxidases, cytochrome bo3 (Cyo) and cytochrome bd (Cyd) oxidase, sustain up to 67% (Cyd) and 78% (Cyo) of HemG activity in the absence of ubiquinone, indicating a tight association of the quinones with the enzyme complexes during preparation 726366 7.1.1.5 physiological function both cytochrome bd-type CydAB, EDC 7.1.1.7, and cytochrome aa3-type menaquinol QoxAB oxidase, EC 7.1.1.5, are used for respiration under different oxygen tensions. Possession of both terminal oxidases is important in infection. In air, the CydAB bd-type oxidase is essential for aerobic respiration and intracellular replication, and cydAB mutants are highly attenuated in mice. At 1% O2 (vol/vol), both oxidases are functional, and the presence of either is sufficient for aerobic respiration and intracellular replication. At 0.2% O2 (vol/vol), both oxidases are necessary for maximum growth -, 750736 7.1.1.5 physiological function cytochrome aa3 is the most important terminal oxidase contributing to proton motive force generation in exponentially growing cells -, 715345 7.1.1.5 physiological function cytochrome aas-600 is the major terminal oxidase in lopgh ase cells -, 715416 7.1.1.5 physiological function demethylmenaquinol in the respiratory chain in the bacterial cytoplasmic membrane is crucial for the extracellular electron transfer. Heme proteins are not involved, and cytochrome bd oxidase activity attenuates extracellular electron transfer 749930 7.1.1.5 physiological function mutants lacking subunits cydA and cydAB are hypersusceptible to compounds targeting the mycobacterial bc1 menaquinol cytochrome c oxidoreductase and exhibit bioenergetic profiles indistinguishable from strains deficient in the ABC-type transporter, CydDC, predicted to be essential for cytochrome bd assembly -, 749594 7.1.1.5 physiological function the enzyme is important during murine infection 742646