According to spectroscopic studies , it has been proposed that the vanadium site in vanadium nitrogenase binds to three sulfides , a homocitrate and a histidine .
The two mechanisms are different in that photosynthesis is an aerobic process - one that requires oxygen - whereas nitrogen fixation , and , consequently , hydrogen production , can take place only anaerobically , because contact with oxygen destroys the nitrogenase enzyme .