TABLE 1. nif gene products and their role (known or proposed) in nitrogen fixation

Gene Identity and/or role of gene product

nifH Fe protein. Obligate electron donor to MoFe protein during nitrogenase turnover. NifH is also required for FeMo-co biosynthesis and apo-MoFe protein maturation.
nifD {alpha} subunit of MoFe protein. Forms an {alpha}2ß2 tetramer with the ß subunit. The site of substrate reduction, FeMo-co, is within the {alpha} subunit of MoFe protein.
nifK ß subunit of MoFe protein. P-clusters are present at each {alpha}ß subunit-interface.
nifT Unknown.
nifY/nafY Chaperone for the apo-MoFe protein. NafY is also a FeMo-co carrier and is proposed to aid in the insertion of FeMo-co into apo-MoFe protein.
nifE Forms {alpha}2ß2 tetramer with NifN. Required for FeMo-co synthesis. Proposed to function as a scaffold on which FeMo-co is synthesized.
nifN Required for FeMo-co synthesis. Tetramer with NifE.
nifX Involved in FeMo-co synthesis. Accumulates an FeSMo-containing precursor.
nifU Molecular scaffold for the formation of Fe-S cluster for nitrogenase components.
nifS Involved in mobilization of S for Fe-S cluster synthesis and repair.
nifV Homocitrate synthase, involved in FeMo-co synthesis.
nifW Involved in stability of MoFe protein.
nifZ Unknown.
nifM Required for the maturation of NifH.
nifF Flavodoxin. Physiological electron donor to NifH in K. pneumoniae.
nifL Negative regulatory element.
nifA Positive regulatory element.
nifB Required for FeMo-co synthesis. Its metabolic product, NifB-co, is a specific Fe and S donor to FeMo-co.
fdxN Ferredoxin. In R. capsulatus, it serves as electron donor to nitrogenase.
nifQ Involved in FeMo-co synthesis. Proposed to function in early MoO42– processing.
nifJ Pyruvate: flavodoxin (ferredoxin) oxidoreductase. Electron donor to Fe protein in K. pneumoniae.