MetaCyc Enzyme: assimilatory nitrite reductase

Gene: nit-6 Accession Number: G-9620 (MetaCyc)

Synonyms: NAD(P)H-nitrite reductase, nitrite reductase [NAD(P)H]

Species: Neurospora crassa

Subunit composition of assimilatory nitrite reductase = [Nit-6]2
         nitrite reductase subunit = Nit-6

Nitrite reductase from Neurospora crassa shows significant amino acid sequence homology with the enzymes from Escherichia coli and Aspergillus nidulans FGSC A4 [Exley93]. The enzyme contains siroheme, non-heme iron in iron-sulfur clusters, and FAD [Prodouz81].

The native molecular weight was determined by gel filtration chromatography and sucrose density gradient centrifugation [Lafferty74].
The subunit molecular weight was determined by SDS-PAGE. The isoelectric point determined for the monomeric subunit was 6.8-6.9 [Prodouz81].

Molecular Weight of Polypeptide: 127.37 kD (from nucleotide sequence), 140 kD (experimental) [Prodouz81 ]

Molecular Weight of Multimer: 290 kD (experimental) [Lafferty74]

Unification Links: Protein Model Portal:P38681 , String:5141.NCU04720.1 , UniProt:P38681

Relationship Links: Entrez-Nucleotide:PART-OF:L07391 , InterPro:IN-FAMILY:IPR001327 , InterPro:IN-FAMILY:IPR005117 , InterPro:IN-FAMILY:IPR006066 , InterPro:IN-FAMILY:IPR006067 , InterPro:IN-FAMILY:IPR007419 , InterPro:IN-FAMILY:IPR012744 , InterPro:IN-FAMILY:IPR013027 , InterPro:IN-FAMILY:IPR017941 , InterPro:IN-FAMILY:IPR023753 , Pfam:IN-FAMILY:PF00070 , Pfam:IN-FAMILY:PF00355 , Pfam:IN-FAMILY:PF01077 , Pfam:IN-FAMILY:PF03460 , Pfam:IN-FAMILY:PF04324 , Pfam:IN-FAMILY:PF07992 , Prints:IN-FAMILY:PR00368 , Prints:IN-FAMILY:PR00397 , Prosite:IN-FAMILY:PS00365 , Prosite:IN-FAMILY:PS51296

Gene-Reaction Schematic: ?

Gene-Reaction Schematic

Instance reaction of [ammonium + 3 NAD(P)+ + 2 H2O ← nitrite + 3 NAD(P)H + 5 H+] (
i1: ammonium + 3 NAD+ + 2 H2O ← nitrite + 3 NADH + 5 H+ (

Created 28-Sep-2006 by Fulcher CA , SRI International

Enzymatic reaction of: nitrite reductase

EC Number:

ammonium + 3 NAD(P)+ + 2 H2O <=> nitrite + 3 NAD(P)H + 5 H+

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.

The reaction is favored in the opposite direction.

Alternative Substrates for nitrite: hydroxylamine [Greenbaum78 ]

In Pathways: nitrate reduction V (assimilatory) , alkylnitronates degradation

This enzyme catalyzes the reduction of nitrite to ammonia in a NADPH-dependent, six-electron transfer reaction. The siroheme prosthetic group is involved in the catalysis and may bind nitrite. NADH can replace NADPH as an electron donor, but NADPH is preferred [Greenbaum78]. Inhibition of the enzyme by carbon monoxide requires the presence of NADPH, and is not complete unless FAD is added [Vega75].

Cofactors or Prosthetic Groups: a [4Fe-4S] iron-sulfur cluster [Prodouz81], siroheme [Vega75], FAD [Prodouz81]

Inhibitors (Competitive): hydrogen cyanide [Lafferty74] , hydrogen sulfite [Lafferty74]

Inhibitors (Noncompetitive): o-phenanthroline [Lafferty74] , HS- [Lafferty74]

Regulators of Unknown Type: carbon monoxide [Vega75]

Kinetic Parameters:

Km (μM)

pH(opt): 7.5 [Lafferty74]


Exley93: Exley GE, Colandene JD, Garrett RH (1993). "Molecular cloning, characterization, and nucleotide sequence of nit-6, the structural gene for nitrite reductase in Neurospora crassa." J Bacteriol 175(8);2379-92. PMID: 8096840

Greenbaum78: Greenbaum P, Prodouz KN, Garrett RH (1978). "Preparation and some properties of homogeneous Neurospora crassa assimilatory NADPH-nitrite reductase." Biochim Biophys Acta 526(1);52-64. PMID: 150863

Lafferty74: Lafferty MA, Garrett RH (1974). "Purification and properties of the Neurospora crassa assimilatory nitrite reductase." J Biol Chem 249(23);7555-67. PMID: 4154942

Prodouz81: Prodouz KN, Garrett RH (1981). "Neurospora crassa NAD(P)H-nitrite reductase. Studies on its composition and structure." J Biol Chem 256(18);9711-7. PMID: 6457037

Vega75: Vega JM, Garrett RH (1975). "Siroheme: a prosthetic group of the Neurospora crassa assimilatory nitrite reductase." J Biol Chem 250(20);7980-9. PMID: 126995

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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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