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| NO2- + 4 H+ + 6 ferricytochrome c = NH4+ + 6 ferrocytochrome c + 2 H2O | | NO2- + 4 H+ + 6 ferricytochrome c = NH4+ + 6 ferrocytochrome c + 2 H2O |
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| The physiological form of the enzyme is believed to be a double trimer of 2 NrfA and 1 NrfH subunits ([[2j7a]]<ref>pmid 17139260 | | The physiological form of the enzyme is believed to be a double trimer of 2 NrfA and 1 NrfH subunits ([[2j7a)]]<ref>pmid 17139260 |
| </ref>). The catalytic subunit NrfA is a pentaheme cytochrome c where the short distances between <scene name='CcNiR/Hemes3/5'>hemes</scene> allow a fast and efficient electron transfer: the active site(<scene name='CcNiR/Heme1/1'>heme1</scene>) 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<ref>pmid 17139260 | | </ref>. The catalytic subunit NrfA is a pentaheme cytochrome c where the short distances between <scene name='CcNiR/Hemes3/5'>hemes</scene> allow a fast and efficient electron transfer: the active site(<scene name='CcNiR/Heme1/1'>heme1</scene>) 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. |
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Revision as of 13:20, 6 September 2012
Your Heading Here ('ccNiR')
The cytochrome 𝑐 nitrite reductase (ccNiR) from Desulfovibrio desulfuricans ATCC 27774 is able to reduce nitrite to ammonia in a six-electron transfer reaction[1] [2] [3] [4] [5] [6]:
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)[7]. 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.
- ↑ Almeida MG, Macieira S, Goncalves LL, Huber R, Cunha CA, Romao MJ, Costa C, Lampreia J, Moura JJ, Moura I. The isolation and characterization of cytochrome c nitrite reductase subunits (NrfA and NrfH) from Desulfovibrio desulfuricans ATCC 27774. Re-evaluation of the spectroscopic data and redox properties. Eur J Biochem. 2003 Oct;270(19):3904-15. PMID:14511372
- ↑ Cunha CA, Macieira S, Dias JM, Almeida G, Goncalves LL, Costa C, Lampreia J, Huber R, Moura JJ, Moura I, Romao MJ. Cytochrome c nitrite reductase from Desulfovibrio desulfuricans ATCC 27774. The relevance of the two calcium sites in the structure of the catalytic subunit (NrfA). J Biol Chem. 2003 May 9;278(19):17455-65. Epub 2003 Mar 4. PMID:12618432 doi:10.1074/jbc.M211777200
- ↑ Costa C, Moura JJ, Moura I, Wang Y, Huynh BH. Redox properties of cytochrome c nitrite reductase from Desulfovibrio desulfuricans ATCC 27774. J Biol Chem. 1996 Sep 20;271(38):23191-6. PMID:8798514
- ↑ Almeida MG, Silveira CM, Guigliarelli B, Bertrand P, Moura JJ, Moura I, Leger C. A needle in a haystack: the active site of the membrane-bound complex cytochrome c nitrite reductase. FEBS Lett. 2007 Jan 23;581(2):284-8. Epub 2006 Dec 19. PMID:17207484 doi:10.1016/j.febslet.2006.12.023
- ↑ Silveira CM, Besson S, Moura I, Moura JJ, Almeida MG. Measuring the cytochrome C nitrite reductase activity-practical considerations on the enzyme assays. Bioinorg Chem Appl. 2010. pii: 634597. Epub 2010 Jun 22. PMID:20689707 doi:10.1155/2010/634597
- ↑ Almeida MG, Silveira CM, Guigliarelli B, Bertrand P, Moura JJ, Moura I, Leger C. A needle in a haystack: the active site of the membrane-bound complex cytochrome c nitrite reductase. FEBS Lett. 2007 Jan 23;581(2):284-8. Epub 2006 Dec 19. PMID:17207484 doi:10.1016/j.febslet.2006.12.023
- ↑ Rodrigues ML, Oliveira TF, Pereira IA, Archer M. X-ray structure of the membrane-bound cytochrome c quinol dehydrogenase NrfH reveals novel haem coordination. EMBO J. 2006 Dec 13;25(24):5951-60. Epub 2006 Nov 30. PMID:17139260
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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).
