NifH/frxC family (IPR000392)

Short name: NifH/frxC

Family relationships


This entry represents members of the NifH/frxC family.

Nitrogen fixing bacteria possess a nitrogenase enzyme complex that catalyses the reduction of molecular nitrogen to ammonia [PMID: 2672439, PMID: 6327620]. The nitrogenase enzyme complex consists of two components:

  • Component I is nitrogenase MoFe protein or dinitrogenase, which contains 2 molecules each of 2 non-identical subunits.
  • Component II is nitrogenase Fe protein or dinitrogenase reductase, which is a homodimer. The monomer is encoded by the NifH gene [PMID: 6327620].

Component II has 2 ATP-binding domains and one 4Fe-4S cluster per homodimer: it supplies energy by ATP hydrolysis, and transfers electrons from reduced ferredoxin or flavodoxin to component I for the reduction of molecular nitrogen to ammonia [PMID: 2491672]. There are a number of conserved regions in the sequence of these proteins: in the N-terminal section there is an ATP-binding site motif 'A' (P-loop) and in the central section there are two conserved cysteines which have been shown, in NifH, to be the ligands of the 4Fe-4S cluster.

Protochlorophyllide reductase is involved in light-independent chlorophyll biosynthesis. The light-independent reaction uses Mg-ATP and reduced ferredoxin to reduce ring D of protochlorophyllide (Pchlide) to form chlorophyllide a (Chlide). This enzyme complex is composed of three subunits: ChlL, ChlN and ChlB. ChlL (also known as frxC) is present as a homodimer, and binds one 4Fe-4S cluster per dimer. The conserved domains, including the ATP-binding motif and the Fe-S binding motif found in the three subunits, are similar to those in nitrogenases [PMID: 16889380].

GO terms

Biological Process

GO:0055114 oxidation-reduction process

Molecular Function

GO:0005524 ATP binding
GO:0016491 oxidoreductase activity

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.
PROSITE profiles