An enzyme complex (EC 1.18.6.1) from bacteria that catalyzes the reduction of dinitrogen to ammonia: N2 + 8e- +10H+ 
2 +NH4 + H2 with the simultaneous hydrolysis of at least 16 ATP molecules. The electron donor is reduced ferredoxin or flavodoxin. Dihydrogen is always a co-product of the reaction. Ethyne (acetylene) can also be reduced to ethene (ethylene) and in some cases ethane. All nitrogenases are iron-sulfur proteins. Three different types which differ in the type of cofactor present, have been identified: molybdenum-nitrogenase (the most common, which contains the iron-molybdenum cofactor), vanadium-nitrogenase, and iron-only nitrogenase. See also FeMo-cofactor.
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