NarGHI complex

GO:0044799 · Energy complex · Multiprotein complex · Proposed

A cytoplasmic membrane-bound NarGHI nitrate reductase complex with iron-sulfur, heme, and molybdenum-bis(molybdopterin guanine dinucleotide) cofactors that serves as a terminal reductase during anaerobic nitrate respiration. [GO:0044799]

Synonyms: cytoplasmic membrane-bound quinol-nitrate oxidoreductase; nitrate reductase A; Nitrate reductase A complex

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Essential	Role
nitrate reductase alpha subunit	Protein	part of	`InterPro:IPR006468`	narG	ESSENTIAL	Molybdenum-bis(molybdopterin guanine dinucleotide)-binding catalytic alpha subunit that accepts electrons from NarH and reduces nitrate to nitrite. `InterPro:IPR006468` InterPro IPR006468 is an exact family entry named Nitrate reductase alpha subunit and integrates the NCBIfam:TIGR01580 NarG HMM. `ComplexPortal:CPX-1974` Complex Portal CPX-1974 curates P09152/NarG as an E. coli K-12 Nitrate reductase A complex participant.
nitrate reductase beta subunit	Protein	part of	`InterPro:IPR006547`	narH	ESSENTIAL	Iron-sulfur beta subunit that relays electrons between the membrane NarI cytochrome and the NarG molybdenum catalytic subunit. `InterPro:IPR006547` InterPro IPR006547 is an exact family entry named Nitrate reductase, beta subunit and integrates the NCBIfam:TIGR01660 NarH HMM. `ComplexPortal:CPX-1974` Complex Portal CPX-1974 curates P11349/NarH as an E. coli K-12 Nitrate reductase A complex participant.
respiratory nitrate reductase subunit gamma	Protein	part of	`NCBIfam:TIGR00351`	narI	ESSENTIAL	Membrane b-type cytochrome gamma subunit that anchors the NarGHI complex and transfers electrons from quinol to NarH. `NCBIfam:TIGR00351` The NCBIfam TIGR00351 model is named respiratory nitrate reductase subunit gamma and has short name narI. `ComplexPortal:CPX-1974` Complex Portal CPX-1974 curates P11350/NarI as an E. coli K-12 Nitrate reductase A complex participant.

Organism-specific protein examples

Named proteins in which each component's role was established, with the organism the evidence comes from. The component above is the taxon-agnostic family; these are the specific entries behind it.

nitrate reductase alpha subunit

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P09152`	Respiratory nitrate reductase 1 alpha chain	narG	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) `UniProtKB:P09152` Reviewed Swiss-Prot entry NARG_ECOLI is the E. coli K-12 NarG alpha chain and cross-references GO:0044799 and ComplexPortal:CPX-1974.

nitrate reductase beta subunit

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P11349`	Respiratory nitrate reductase 1 beta chain	narH	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) `UniProtKB:P11349` Reviewed Swiss-Prot entry NARH_ECOLI is the E. coli K-12 NarH beta chain and cross-references GO:0044799 and ComplexPortal:CPX-1974.

respiratory nitrate reductase subunit gamma

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P11350`	Respiratory nitrate reductase 1 gamma chain	narI	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) `UniProtKB:P11350` Reviewed Swiss-Prot entry NARI_ECOLI is the E. coli K-12 NarI gamma chain and cross-references GO:0044799 and ComplexPortal:CPX-1974.

Source composition assertions

Nitrate reductase A complex (ComplexPortal:CPX-1974)

Escherichia coli (strain K12) (NCBITaxon:83333) · Heterohexamer · ECO:0000353 · retrieved 2026-10-02

Participant	Source type	Source name	Stoichiometry
`CHEBI:21137` — tri-mu-sulfido-mu3-sulfido-triiron	small molecule		2
`CHEBI:60539` — Mo(=O)-bis(molybdopterin guanine dinucleotide)(4-)	small molecule		2
`CHEBI:49883` — tetra-mu(3)-sulfido-tetrairon (IRON/SULFUR CLUSTER)	small molecule		8
`UniProtKB:P09152` — Respiratory nitrate reductase 1 alpha chain	protein	narG	2
`UniProtKB:P11349` — Respiratory nitrate reductase 1 beta chain	protein	narH	2
`UniProtKB:P11350` — Respiratory nitrate reductase 1 gamma chain	protein	narI	2
`CHEBI:30413` — heme	small molecule		4

Curator-scoped import: E. coli K-12 Nitrate reductase A composition for the GO:0044799 NarGHI complex. Source evidence: physical interaction evidence. The accession was resolved through the Complex Portal accession endpoint; no equivalence xref was inferred.

Canonical examples

NCBITaxon:83333 Escherichia coli K-12 — Escherichia coli K-12 source of the CPX-1974 NarGHI heterohexamer with NarG, NarH, NarI, heme, iron-sulfur, and Mo-bis(molybdopterin guanine dinucleotide) participants. [ComplexPortal:CPX-1974]

Functions

nitrate reductase (quinone) activity GO:0160182 — The NarGHI complex oxidizes quinol to quinone while reducing nitrate to nitrite during anaerobic nitrate respiration.
- GO:0160182 GO:0160182 defines quinol-dependent nitrate reductase activity as catalysis of quinol plus nitrate to quinone, water, and nitrite.
- PMID:12910261 Bertero et al. 2003 structurally traced the NarGHI respiratory electron-transfer route from NarI through NarH to the NarG Mo-bisMGD catalytic site.

Mechanism graphs

NarGHI routes quinol electrons to nitrate (FUNCTION)

NarI accepts quinol-derived electrons through hemes and passes them through NarH iron-sulfur centers to the NarG Mo-bisMGD site that reduces nitrate to nitrite.

Subject	Predicate	Object	Evidence
respiratory nitrate reductase subunit gamma	receives electrons from	quinol	`GO:0044799` GO:0044799 states that NarGHI electrons pass from NarI hemes down a NarH/NarG iron-sulfur chain.
nitrate reductase beta subunit	relays electrons toward	nitrate reductase alpha subunit	`GO:0044799` GO:0044799 places NarH between the NarI hemes and the Mo-bisMGD cofactor in NarG.
nitrate	accepts electrons in	nitrate reductase (quinone) activity	`GO:0160182` GO:0160182 defines the reaction as quinol plus nitrate yielding quinone, water, and nitrite.
respiratory nitrate reductase subunit gamma	contributes to	nitrate reductase (quinone) activity	`PMID:12910261` Bertero et al. 2003 resolved the NarI transmembrane electron-entry subunit in the nitrate reductase A structure.
NarGHI complex	enables	nitrate reductase (quinone) activity	`GO:0044799` GO:0044799 defines NarGHI as the terminal reductase in anaerobic nitrate-respiration electron transport. `ComplexPortal:CPX-1974` Complex Portal CPX-1974 curates the E. coli K-12 NarGHI nitrate reductase A complex.

Evidence

GO:0044799 Gene Ontology cellular-component term for the NarGHI complex.
GO:0009325 Gene Ontology parent cellular-component term for nitrate reductase complexes.
GO:0160182 Gene Ontology molecular-function term for quinol-dependent nitrate reductase activity.
InterPro:IPR006468 InterPro family for the NarG nitrate reductase alpha subunit.
InterPro:IPR006547 InterPro family for the NarH nitrate reductase beta subunit.
NCBIfam:TIGR00351 NCBIfam HMM for the NarI respiratory nitrate reductase gamma subunit.
UniProtKB:P09152 Reviewed E. coli K-12 NarG alpha-chain UniProtKB entry.
UniProtKB:P11349 Reviewed E. coli K-12 NarH beta-chain UniProtKB entry.
UniProtKB:P11350 Reviewed E. coli K-12 NarI gamma-chain UniProtKB entry.
ComplexPortal:CPX-1974 Complex Portal entry for the E. coli K-12 Nitrate reductase A complex.
CHEBI:21137 ChEBI identifier for the 3Fe-4S cofactor curated as a CPX-1974 small-molecule participant.
CHEBI:49883 ChEBI identifier for the 4Fe-4S cofactor curated as a CPX-1974 small-molecule participant.
CHEBI:60539 ChEBI identifier for Mo-bis(molybdopterin guanine dinucleotide), the NarG molybdenum cofactor curated in CPX-1974.
CHEBI:30413 ChEBI identifier for the CPX-1974 heme participants.
PMID:12910261 Bertero et al. 2003, Insights into the respiratory electron transfer pathway from the structure of nitrate reductase A.
DOI:10.1038/nsb969 DOI for the Bertero et al. 2003 NarGHI structure paper.
PMID:11289299 Moreno-Vivian et al. 2001, Functional, biochemical and genetic diversity of prokaryotic nitrate reductases.
DOI:10.1007/PL00000845 DOI for the Moreno-Vivian et al. 2001 nitrate reductase review.
PMID:17964535 Jormakka et al. 2008, The prokaryotic complex iron-sulfur molybdoenzyme family.
DOI:10.1016/j.bbamem.2007.09.002 DOI for the Jormakka et al. 2008 review cited by GO:0044799.

Curation history

2026-10-02T04:14:47Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-10-02T04:16:24Z codex · EXPANDED_RECORD — Added GO/Complex Portal synonymy and parentage, NarG/NarH/NarI component rows with exact family groundings and E. coli K-12 UniProt examples, a CPX-1974 heterohexamer composition with cofactors, quinol:nitrate oxidoreductase activity, primary literature/database evidence, and a compact NarI-to-NarH-to-NarG electron-transfer graph.

Source: data/structures/energy_complex/narghi_complex.yaml