MetaCyc Enzyme: periplasmic nitrate reductase (cytochrome)

Superclasses: a nitrate reductaseA Prokaryotic Periplasmic Nitrate Reductase

Species: Aliivibrio fischeri

Subunit composition of periplasmic nitrate reductase (cytochrome) = [NapA][NapB]
         nitrate reductase large subunit = NapA
         nitrate reductase small subunit = NapB

General Background

Four classes of nitrate reductases are known - a eukaryotic class, and three prokaryotic classes. The eukaryotic nitrate reductases are found in plants, algae and fungi, and are involved in assimilation of nitrate. They are composed of two identical subunits, and contain a MoO2-molybdopterin cofactor and an FAD prosthetic group. In general, plant enzymes prefer NADH as the electron donor ( EC and fungal enzymes prefer NADPH ( EC, although some enzymes were reported to accept either of these compounds ( EC [Beevers64]. Example for eukaryotic enzymes include the assimilatory nitrate reductase (NADH) from Arabidopsis thaliana col and the assimilatory nitrate reductase (NADPH) from Neurospora crassa.

Prokaryotic nitrate reductases are divided into three classes, including a class of assimilatory enzymes and two classes of respiratory enzymes. All of them include a guanylyl molybdenum cofactor cofactor, but differ in their substructures, cellular location, and cofactor requirement. Variabillity among enzymes is also found within the classes. Assimilatory prokaryotic nitrate reductases (NAS) are involved in the assimilation of nitrogen from nitrate for incorporation into protein. Despite their relatedness, these enzymes vary in their substructures and cofactors. For example, assimilatory nitrate reductase [NAD(P)H] from Klebsiella oxytoca M5al is a heterodimer that utilizes NAD(P)H, while ferredoxin--nitrate reductase from the cyanobacterium Synechococcus elongatus PCC 7942 and assimilatory nitrate reductase from the Gram-negative bacterium Azotobacter vinelandii are monomeric and utilize ferredoxin ( EC and flavodoxin, respectively.

Respiratory nitrate reductases use nitrate as the electron acceptor of an anaerobic respiratory chain which usually starts with the quinone pool ( EC One of these classes (NAR) consists of membrane-bound enzymes that are composed of three different subunits. These enzymes, which include respiratory nitrate reductase from Pseudomonas stutzeri and the Escherichia coli K-12 enzymes nitrate reductase A and nitrate reductase Z, are anchored to the cytoplasmic membrane, with the active site facing the cytoplasm.

The second class of bacterial respiratory nitrate reductases (NAP) consists of periplasmic enzymes, which are usually heterodimers, although monomeric forms have been reported. Examples for enzymes belonging to this class include periplasmic nitrate reductase from Escherichia coli K-12 ( EC and periplasmic nitrate reductase (cytochrome) from Aliivibrio fischeri ( EC

About This Protein

This nitrate reductase of Aliivibrio fischeri has been investigated in detail by Sadana and McElroy, who found that electrons arriving from NAD(P)H were routed via an FAD cofactor and an iron-sulfur center to a specific cytochrome-nitrate reductase [Sadana57]. The sequencing of the genome of Aliivibrio fischeri revealed that the enzyme is a member of the periplasmic dissimilatory nitrate reductases, a class of enzymes that is usually composed of two different subunits. The large subunit, encoded by napA, contains a guanylyl molybdenum cofactor cofactor and a single a [4Fe-4S] iron-sulfur cluster, while the small subunit, encoded by napB, contains two c-type hemes [Richardson01]. The NapAB complex receives the electrons from NapC, a tetra-heme c-type cytochrome encoded by the napC gene [Gonzalez06a].

Locations: periplasm

Molecular Weight: 100.0 kD (experimental) [Sadana57]

Gene-Reaction Schematic

Gene-Reaction Schematic

GO Terms:
Cellular Component:
GO:0030288 - outer membrane-bounded periplasmic space []

Created 12-Oct-2007 by Caspi R, SRI International

Enzymatic reaction of: nitrate reductase

Inferred from experiment

EC Number:

Transport reaction diagram for nitrate reductase

In Pathways: nitrate reduction IV (dissimilatory)

The enzyme catalyzed the reduction of 600 moles nitrate/mole protein/min [Sadana57].

Cofactors or Prosthetic Groups: a [4Fe-4S] iron-sulfur cluster [Richardson01], guanylyl molybdenum cofactor [Richardson01], a c-type cytochrome [Richardson01]

pH(opt): 7-8.5 [Sadana57]

Subunit of periplasmic nitrate reductase (cytochrome): nitrate reductase large subunit

Synonyms: NapA

Gene: napA Accession Number: G-10237 (MetaCyc)

Molecular Weight: 92.594 kD (from nucleotide sequence)

Unification Links: Protein Model Portal:Q5E3J6, SMR:Q5E3J6, UniProt:Q5E3J6

Relationship Links: InterPro:IN-FAMILY:IPR006311, InterPro:IN-FAMILY:IPR006656, InterPro:IN-FAMILY:IPR006657, InterPro:IN-FAMILY:IPR006963, InterPro:IN-FAMILY:IPR009010, InterPro:IN-FAMILY:IPR010051, InterPro:IN-FAMILY:IPR027467, Pfam:IN-FAMILY:PF00384, Pfam:IN-FAMILY:PF01568, Pfam:IN-FAMILY:PF04879, Prosite:IN-FAMILY:PS00551, Prosite:IN-FAMILY:PS51318, Prosite:IN-FAMILY:PS51669, Smart:IN-FAMILY:SM00926

Subunit of periplasmic nitrate reductase (cytochrome): nitrate reductase small subunit

Synonyms: NapB, cytochrome c-type protein NapB

Gene: napB Accession Number: G-10238 (MetaCyc)

Molecular Weight: 17.488 kD (from nucleotide sequence)

Unification Links: Protein Model Portal:Q5E3J7, UniProt:Q5E3J7

Relationship Links: InterPro:IN-FAMILY:IPR005591, InterPro:IN-FAMILY:IPR011031, InterPro:IN-FAMILY:IPR027406, Pfam:IN-FAMILY:PF03892, Prosite:IN-FAMILY:PS51008


Beevers64: Beevers, L, Flesher, D., Hageman, R.H. (1964). "Studies on the pyridine nucleotide specificity of nitrate reductase in higher plants and its relationship to sulfhydryl level." Biochim Biophys Acta 89:453-64. PMID: 14209328

Gonzalez06a: Gonzalez PJ, Correia C, Moura I, Brondino CD, Moura JJ (2006). "Bacterial nitrate reductases: Molecular and biological aspects of nitrate reduction." J Inorg Biochem 100(5-6);1015-23. PMID: 16412515

Park06: Park YJ, Yoo CB, Choi SY, Lee HB (2006). "Purifications and characterizations of a ferredoxin and its related 2-oxoacid:ferredoxin oxidoreductase from the hyperthermophilic archaeon, Sulfolobus solfataricus P1." J Biochem Mol Biol 39(1);46-54. PMID: 16466637

Richardson01: Richardson DJ, Berks BC, Russell DA, Spiro S, Taylor CJ (2001). "Functional, biochemical and genetic diversity of prokaryotic nitrate reductases." Cell Mol Life Sci 58(2);165-78. PMID: 11289299

Sadana57: Sadana, J.C., McElroy, W.D. (1957). "Nitrate reductase from Achromobacter fischeri; purification and properties: function of flavines and cytochrome." Arch Biochem Biophys 67(1);16-34. PMID: 13412117

Report Errors or Provide Feedback
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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