This molybdenum-iron protein is part of the nitrogenase complex that catalyzes the key enzymatic reactions in nitrogen fixation. 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 [8Fe-7S] cluster per heterodimer. Tetramer of two alpha and two beta chains. Forms complex with the iron protein (nitrogenase component 2). Ala-187 is present instead of the usual Ser that would serve as a ligand for the 8Fe-7S cluster in the oxidized state. Belongs to the NifD/NifK/NifE/NifN family.