nitrogenase complex

GO:0016610 · Energy complex · Multiprotein complex · Proposed

A nitrogenase enzyme complex composed of tetrameric dinitrogenase and homodimeric nitrogenase reductase subcomplexes that together catalyze ATP-dependent reduction of dinitrogen to ammonia. [GO:0016610]

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

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
dinitrogenase	Protein complex	part of	Reviewed label only (reviewed name; no accession asserted)			ESSENTIAL	Tetrameric metal-cluster subcomplex required with nitrogenase reductase for nitrogenase activity. `GO:0016610` GO:0016610 defines nitrogenase as containing a tetrameric dinitrogenase protein component. `PDB:1N2C` The PDB:1N2C deposition maps two polymer entities to the Azotobacter vinelandii molybdenum-iron dinitrogenase alpha and beta chains.
nitrogenase reductase	Protein complex	part of	Reviewed label only (reviewed name; no accession asserted)			ESSENTIAL	Homodimeric ATP-dependent reductase subcomplex required with dinitrogenase for nitrogenase activity. `GO:0016610` GO:0016610 defines nitrogenase as containing a homodimeric nitrogenase reductase protein component. `PDB:1N2C` The PDB:1N2C deposition maps polymer entity 3 to Azotobacter vinelandii NifH1, the molybdenum nitrogenase iron protein.

Canonical examples

NCBITaxon:354 Azotobacter vinelandii — Bacterial source of the molybdenum-iron dinitrogenase and iron-protein reductase assembly deposited as PDB:1N2C. [PDB:1N2C]

Functions

nitrogenase activity GO:0016163 — Nitrogenase couples ATP hydrolysis and reduced-ferredoxin oxidation to reduction of dinitrogen, producing ammonium and dihydrogen.
- GO:0016163 GO:0016163 defines nitrogenase activity as the ATP-dependent reduced-ferredoxin:dinitrogen oxidoreductase reaction.
- DOI:10.1038/387370a0 Schindelin et al. 1997 reported an Azotobacter vinelandii nitrogenase complex stabilized in a state containing the MoFe protein and Fe protein.

Mechanism graphs

Nitrogenase couples ATP to dinitrogen reduction (FUNCTION)

The nitrogenase complex couples ATP hydrolysis and reduced-ferredoxin oxidation to dinitrogen reduction through required dinitrogenase and nitrogenase reductase subcomplexes.

Subject	Predicate	Object	Evidence
reduced ferredoxin	donates electrons to	nitrogenase activity	`GO:0016163` GO:0016163 records reduced ferredoxin as the electron donor oxidized during nitrogenase activity.
ATP	is hydrolyzed by	nitrogenase activity	`GO:0016163` GO:0016163 defines the nitrogenase reaction as consuming ATP and water and producing ADP and phosphate.
nitrogenase reductase	docks with	dinitrogenase	`PDB:1N2C` PDB:1N2C captures A. vinelandii nitrogenase reductase chains bound to the MoFe dinitrogenase protein.
nitrogenase reductase	contributes to	nitrogenase activity	`GO:0016610` GO:0016610 defines both dinitrogenase and nitrogenase reductase as required for nitrogenase complex enzyme activity.
dinitrogenase	contributes to	nitrogenase activity	`GO:0016610` GO:0016610 defines both dinitrogenase and nitrogenase reductase as required for nitrogenase complex enzyme activity.
dinitrogen	accepts electrons in	nitrogenase activity	`GO:0016163` GO:0016163 records dinitrogen as the acceptor in nitrogenase activity.
nitrogenase activity	produces	ammonium	`GO:0016163` GO:0016163 records two ammonium products in the nitrogenase reaction.
nitrogenase activity	produces	dihydrogen	`GO:0016163` GO:0016163 records H2 as a product of nitrogenase activity.

Discussions

CURATION_TODO (OPEN): Resolve variant-specific Mo-Fe, V-Fe, and Fe-Fe dinitrogenase and reductase groundings before replacing the generic reviewed-label-only component rows. GO:0016610 exactly grounds the complete nitrogenase complex across multiple metal variants; the verified InterPro terms cover narrower molybdenum-iron NifD, NifK, and NifH families or broader families that also include non-nitrogenase proteins.

Evidence

GO:0016610 Gene Ontology cellular-component term for the generic nitrogenase complex.
GO:0140535 Gene Ontology cellular-component term for intracellular protein-containing complexes.
GO:1990204 Gene Ontology cellular-component term for oxidoreductase complexes.
GO:0016163 Gene Ontology molecular-function term for nitrogenase activity.
DOI:10.1038/387370a0 Schindelin et al. 1997, Structure of ADP x AlF4(-)-stabilized nitrogenase complex and its implications for signal transduction, Nature.
PMID:9163420 PubMed identifier for Schindelin et al. 1997 as reported by the RCSB PDB:1N2C primary citation.
PDB:1N2C RCSB Protein Data Bank entry for the Azotobacter vinelandii nitrogenase complex structure from Schindelin et al. 1997.

Curation history

2026-09-24T04:40:50Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-24T04:41:30Z codex · EXPANDED_RECORD — Added oxidoreductase-complex parentage, reviewed-label-only dinitrogenase and nitrogenase reductase components, an Azotobacter PDB:1N2C canonical example, GO nitrogenase activity, primary Schindelin et al. literature/PDB evidence, a compact nitrogenase function graph, and a component-grounding TODO.
2026-09-24T04:42:10Z codex · NARROWED_GRAPH_EDGE — Replaced the under-supported nitrogenase reductase-to-dinitrogenase electron-transfer edge with GO:0016610-supported contribution edges from both required nitrogenase subcomplexes to nitrogenase activity.
2026-09-24T04:42:50Z codex · TIGHTENED_GRAPH_WORDING — Tightened generic nitrogenase component and graph wording to required subcomplex contribution claims and duplicated the shared GO evidence list to avoid YAML anchors.
2026-09-24T04:53:24Z codex · RESOLVED_REVIEW_ISSUE — Resolved issue #1450 by aligning the GO:0016163-backed nitrogenase activity product wording with ammonium in the function description and causal graph node/edge.

Source: data/structures/energy_complex/nitrogenase_complex.yaml