Cytochrome c nitrite reductase

{{Short description|Class of enzymes}}

{{infobox enzyme

| Name = Cytochrome c nitrite reductase

| EC_number = 1.7.2.2

| CAS_number =

| GO_code = 0042279

| image = 1GU6.png

| PDB = 1GU6

| width =

| caption = Crystallographic structure of a homodimer of the cytochrome c nitrite reductase from Escherichia coli (rainbow colored cartoon, blue = N-terminus, red = C-terminus) complexed with heme C (sticks).{{PDB|1GU6}}; {{cite journal | vauthors = Bamford VA, Angove HC, Seward HE, Thomson AJ, Cole JA, Butt JN, Hemmings AM, Richardson DJ | title = Structure and spectroscopy of the periplasmic cytochrome c nitrite reductase from Escherichia coli | journal = Biochemistry | volume = 41 | issue = 9 | pages = 2921–31 |date=March 2002 | pmid = 11863430 | doi = 10.1021/bi015765d }}

}}

Cytochrome c nitrite reductase (ccNiR) ({{EC number|1.7.2.2}}) is a bacterial enzyme that catalyzes the six electron reduction of nitrite to ammonia; an important step in the biological nitrogen cycle.{{cite book | vauthors = Clarke TA, Mills PC, Poock SR, Butt JN, Cheesman MR, Cole JA, Hinton JC, Hemmings AM, Kemp G, Söderberg CA, Spiro S, Van Wonderen J, Richardson DJ | chapter = Escherichia coli Cytochrome c Nitrite Reductase NrfA | title = Globins and Other Nitric Oxide-Reactive Proteins, Part B | series = Methods in Enzymology | volume = 437 | pages = 63–77 | year = 2008 | pmid = 18433623 | doi = 10.1016/S0076-6879(07)37004-3 | isbn = 9780123742780 }} The enzyme catalyses the second step in the two step conversion of nitrate to ammonia, which allows certain bacteria to use nitrite as a terminal electron acceptor, rather than oxygen, during anaerobic conditions. During this process, ccNiR draws electrons from the quinol pool, which are ultimately provided by a dehydrogenase such as formate dehydrogenase or hydrogenase. These dehydrogenases are responsible for generating a proton motive force.{{cite journal | author = Simon J | title = Enzymology and bioenergetics of respiratory nitrite ammonification | journal = FEMS Microbiol. Rev. | volume = 26 | issue = 3 | pages = 285–309 |date=August 2002 | pmid = 12165429 | doi = 10.1111/j.1574-6976.2002.tb00616.x| doi-access = free }}

Cytochrome c Nitrite Reductase is a homodimer which contains five c-type heme cofactors per monomer.{{cite journal | vauthors = Einsle O, Messerschmidt A, Stach P, Bourenkov GP, Bartunik HD, Huber R, Kroneck PM | title = Structure of cytochrome c nitrite reductase | journal = Nature | volume = 400 | issue = 6743 | pages = 476–80 |date=July 1999 | pmid = 10440380 | doi = 10.1038/22802 | bibcode = 1999Natur.400..476E | s2cid = 4403452 }} Four of the heme centers are bis-histidine ligated and presumably serve to shuttle electrons to the active site. The active site heme, however, is uniquely ligated by a single lysine residue.

This enzyme belongs to the family of oxidoreductases, specifically those acting on other nitrogenous compounds as donors with a cytochrome as acceptor. The systematic name of this enzyme class is ammonia:ferricytochrome-c oxidoreductase.

{{Infobox protein family

| Symbol = Cytochrom_NNT

| Name = Cytochrom_NNT

| image =

| width =

| caption = crystal structure of cytochrome c nitrite reductase nrfha complex from desulfovibrio vulgaris

| Pfam = PF03264

| Pfam_clan = CL0317

| InterPro = IPR005126

| SMART =

| PROSITE =

| MEROPS =

| SCOP =

| TCDB =

| OPM family = 175

| OPM protein = 2j7a

| CAZy =

| CDD =

}}