PROSITE documentation PDOC00085
Nitrogenases component 1 alpha and beta subunits signatures


Nitrogenase (EC [1] is the enzyme system responsible for biological nitrogen fixation. Nitrogenase is an oligomeric complex which consists of two components: component 2 is an homodimer of an iron-sulfur protein, while component 1 which contains the active site for the reduction of nitrogen to ammonia exists in three different forms:

  • A molybdenum-iron containing protein (MoFe). The MoFe protein is a hetero- tetramer consisting of two pairs of α (nifD) and β (nifK) subunits.
  • A vanadium-iron containing protein (VFe). The VFe protein is a hexamer of two pairs each of α (vnfD), β (vnfK), and delta (vnfG) subunits.
  • The third form of component 1 seems to only contain iron. Like the vanadium form it is a hexamer composed of α (anfD), β (anfK), and delta (anfG) subunits.

The α and β chains of the three types of component 1 are evolutionary related and they are also related to proteins nifE and nifN, which are most probably involved in the iron-molybdenum cofactor biosynthesis [2].

We selected as signature patterns for this family of proteins two stretches of residues which are located in the N-terminal section and which each contain a conserved cysteine thought to be one of the ligands for the metal-sulfur clusters.

Last update:

May 2004 / Text revised.


Technical section

PROSITE methods (with tools and information) covered by this documentation:

NITROGENASE_1_1, PS00699; Nitrogenases component 1 alpha and beta subunits signature 1  (PATTERN)

NITROGENASE_1_2, PS00090; Nitrogenases component 1 alpha and beta subunits signature 2  (PATTERN)


1AuthorsPau R.N.
TitleNitrogenases without molybdenum.
SourceTrends Biochem. Sci. 14:183-186(1989).
PubMed ID2672439

2AuthorsAguilar O.M. Taormino J. Thony B. Ramseier T. Hennecke H. Szalay A.A.
TitleThe nifEN genes participating in FeMo cofactor biosynthesis and genes encoding dinitrogenase are part of the same operon in Bradyrhizobium species.
SourceMol. Gen. Genet. 224:413-420(1990).
PubMed ID2266945

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