CcNiR

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spinqualitylabelsall models CYTOCHROME C NITRITE REDUCTASE FROM DESULFOVIBRIO DESULFURICANS ATCC 27774 (PDB entry 1oah) Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D The cytochrome 𝑐 nitrite reductase (ccNiR) from Desulfovibrio desulfuricans ATCC 27774 is able to reduce nitrite to ammonia in a six-electron transfer reaction : NO2- + 4 H+ + 6 ferricytochrome c = NH4+ + 6 ferrocytochrome c + 2 H2O The physiological form of the enzyme is believed to be a double trimer of 2 NrfA and 1 NrfH subunits (2j7a). The catalytic subunit NrfA is a pentaheme cytochrome c where the short distances between hemes allow a fast and efficient electron transfer: the active site(heme1) has been reported as an unusual lysine-coordinated high-spin heme. NrfH is a small membrane-bound cytochrome comprising four c-type heme groups and it serves a double purpose. On one hand, it anchors the catalytic subunits to the membrane. On the other hand, it serves as a quinol oxidase, transferring electrons from the quinone pool to the catalytic subunits. The overall haem arrangement of the NrfHA complex is rather unusal, comprising 28 hemes in a compact arrangement.

Cytochrome c nitrite reductase is a multicenter enzyme that uses a five-coordinated heme to perform the reduction of nitrite to ammonium in a six-electron transfer reaction. In the sulfate reducing bacterium Desulfovibrio desulfuricans ATCC 27774, the enzyme is purified as a NrfA4NrfH4 complex that houses 28 hemes.

The catalytic reaction occurs at a high-spin (5-coordinated) heme that is located at the pentahemic subunit NrfA which is strongly bound to its physiological electron donor, the smaller hydrophobic polypeptide tetrahemic NrfH, composed of 4 c-types hemes; in vitro, the protein complexes associate each other forming huge aggregates (min. 890 kDa).

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