Found in nitrogen-fixing bacteria and archaea, nitrogenase's primary biological function generates ammonia from dinitrogen. This activity is essential for all organisms because it sequesters nitrogen gas in a biologically accessible form. Throughout the process of ammonia generation by nitrogenase, hydrogen is formed. The enzyme has several forms, which utilize different metals in the catalytic site. These metals evolve various amounts of hydrogen. The three metals characterized are molybdenum, vanadium, and iron. They generate 1, 3, 7.5 moles of hydrogen per mole of nitrogen, respectively [1]. This enzyme is powered by ATP; it requires 2 ATP per hydrogen atom produced [1]. Both the electrons and the ATP in this system are provided through photosynthesis.   Inherently, photosynthesis generates oxygen gas, while concurrently generating protons and electrons. The electrons pass through a series of electron carriers to finally reduce ferredoxin or flavodoxin [1] (these require approxiamately 4 electrons for reduction). In addition to the large energy requirements, a further obstacle for industrial use is nitrogenase is oxygen sensitive.

[1] Prince, R.C., Kheshgi, H.S., 2005, Crit Rev Microbiol 31 , 19-31.