| Description | This family consists of several Cbb3-type cytochrome oxidase components (FixQ/CcoQ). FixQ is found in nitrogen fixing bacteria. Since nitrogen fixation is an energy-consuming process, effective symbioses depend on operation of a respiratory chain with a high affinity for O2, closely coupled to ATP production. This requirement is fulfilled by a special three-subunit terminal oxidase (cytochrome terminal oxidase cbb3), which was first identified in Bradyrhizobium japonicum as the product of the fixNOQP operon [ ].Cytochrome cbb3 oxidase, the terminal oxidase in the respiratory chains of proteobacteria, is a multi-chain transmembrane protein located in the cell membrane. Like other cytochrome oxidases, it catalyses the reduction of O2 and simultaneously pumps protons across the membrane. Found exclusively in proteobacteria, cbb3 is believed to be a modern enzyme that has evolved independently to perform a specialized function in microaerobic energy metabolism [ , , ]. The cbb3 operon contains four genes (ccoNOQP or fixNOQP), with ccoN coding for subunit I []. Instead of a CuA-containing subunit II analogous to other cytochrome oxidases, cbb3 utilizes subunits ccoO and ccoP, which contain one and two hemes, respectively, to transfer electrons to the binuclear centre. ccoQ, the fourth subunit, is a single transmembrane helix protein. It has been shown to protect the core complex from proteolytic degradation by serine proteases []. | Name | Cbb3-type cytochrome oxidase component |
| Short Name | Cbb3-typ_cyt_oxidase_comp | Type | Family |
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