The key enzymatic reactions in nitrogen fixation are catalyzed by the nitrogenase complex, which has 2 components: the iron protein and the molybdenum-iron protein. 16 ATP + 16 H2O + N2 + 8 reduced [2Fe-2S]-[ferredoxin] = 16 ADP + 6 H(+) + H2 + 2 NH4(+) + 8 oxidized [2Fe-2S]-[ferredoxin] + 16 phosphate Binds 1 [4Fe-4S] cluster per dimer. Homodimer. The reversible ADP-ribosylation of Arg-102 inactivates the nitrogenase reductase and regulates nitrogenase activity. Belongs to the NifH/BchL/ChlL family.