Vanadium nitrogenase is a key enzyme for nitrogen fixation found in nitrogen-fixing bacteria, and is used as an alternative to molybdenum nitrogenase when molybdenum is unavailable. An important component of the nitrogen cycle, vanadium nitrogenase converts nitrogen gas to ammonia, thereby making otherwise inaccessible nitrogen available to plants. Unlike molybdenum nitrogenase, vanadium nitrogenase can also reduce carbon monoxide to ethylene, ethane and propane but both enzymes can reduce protons to hydrogen gas and acetylene to ethylene.