Vanadium nitrogenases are found in members of the bacterial genus Azotobacter as well as the species Rhodopseudomonas palustris and Anabaena variabilis. Most of the functions of vanadium nitrogenase match those of the more common molybdenum nitrogenases and serve as an alternative pathway for nitrogen fixation in molybdenum deficient conditions. Like molybdenum nitrogenase, dihydrogen functions as a competitive inhibitor and carbon monoxide functions as a non-competitive inhibitor of nitrogen fixation. Vanadium nitrogenase has an αβΎ subunit structure while molybdenum nitrogenase has an αβ structure. Though the structural genes encoding vanadium nitrogenase show only about 15% conservation with molybdenum nitrogenases, the two nitrogenases share the same type of iron-sulphur redox centers. At room temperature, vanadium nitrogenase is less efficient at fixing nitrogen than molybdenum nitrogenases because it converts more H to H as a side reaction. However, at low temperatures vanadium nitrogenases have been found to be more active than the molybdenum type, and at temperatures as low as 5 °C its nitrogen-fixing activity is 10 times higher than that of molybdenum nitrogenase. Like molybdenum nitrogenase, vanadium nitrogenase is easily oxidized and is thus only active under anaerobic conditions. Various bacteria employ complex protection mechanisms to avoid oxygen.
The overall stoichiometry of nitrogen fixation catalyzed by vanadium nitrogenase can be summarized as follows:
:N + 12e + 14H + 24MgATP → 2NH + 3H + 24MgADP + 24HPO
The crystal structure of A. vinelandii vanadium nitrogenase was resolved in 2017 (). Compared to Mo nitrogenase, V nitrogenase replaces one sulfide in the active site with a bridging ligand.