CcNiR: Difference between revisions

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== 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.

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 ~~periplasmic membrane-associated~~ 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 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. <ref>pmid 14511372</ref> <ref>pmid 12618432</ref> <ref>pmid 8798514</ref> <ref>pmid 17207484</ref> <ref>pmid 20689707</ref> <ref>pmid 17207484</ref>

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 <scene name='CcNiR/Hemes3/5'>hemes</scene> allow a fast and efficient electron transfer: the active site (heme 1) 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.

REFERENCES:

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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).

~~The overall haem arrangement of the NrfHA complex is quite surprising, as the NrfH haem groups are positioned non-symmetrically with respect to the two NrfA molecules.~~

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 == Your Heading Here ('ccNiR') ==
 <StructureSection load='1oah' size='500' side='left' caption='CYTOCHROME C NITRITE REDUCTASE FROM DESULFOVIBRIO DESULFURICANS ATCC 27774 (PDB entry [[1oah]])' scene=''>
-The cytochrome 𝑐 nitrite reductase (ccNiR) from Desulfovibrio desulfuricans ATCC 27774 is able to reduce nitrite to ammonia in a six-electron transfer reaction.
+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 periplasmic membrane-associated 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 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. <ref>pmid 14511372</ref> <ref>pmid 12618432</ref> <ref>pmid 8798514</ref> <ref>pmid 17207484</ref> <ref>pmid 20689707</ref> <ref>pmid 17207484</ref>
+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 <scene name='CcNiR/Hemes3/5'>hemes</scene> allow a fast and efficient electron transfer: the active site (heme 1) 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.
+REFERENCES:
+<ref>pmid 14511372</ref> <ref>pmid 12618432</ref> <ref>pmid 8798514</ref> <ref>pmid 17207484</ref> <ref>pmid 20689707</ref> <ref>pmid 17207484</ref>
@@ Line 16: / Line 20: @@
 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).
-The overall haem arrangement of the NrfHA complex is quite surprising, as the NrfH haem groups are positioned non-symmetrically with respect to the two NrfA molecules.
 <references/>