Nitrogenase component 1, conserved site Nitrogenase (<db_xref db="EC" dbkey="1.18.6.1"/>) [<cite idref="PUB00005343"/>] 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-sulphur protein, while component 1 which contains the active site for the reduction of nitrogen to ammonia exists in three different forms: the molybdenum-iron containing protein (MoFe) is a hetero-tetramer consisting of two pairs of alpha (nifD) and beta (nifK) subunits; the vanadium-iron containing protein (VFe) is a hexamer of two pairs each of alpha (vnfD), beta (vnfK), and delta (vnfG) subunits; the third form seems to only contain iron and is a hexamer composed of alpha (anfD), beta (anfK), and delta (anfG) subunits.The alpha and beta 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 [<cite idref="PUB00003737"/>].