How many protons and electrons are required to fix a dinitrogen?

In nitrogen-fixing microorganisms, the eight high-potential electrons come from reduced ferredoxin, generated by photosynthesis or oxidative processes. Two molecules of ATP are hydrolyzed for each electron transferred. Thus, at least 16 molecules of ATP are hydrolyzed for each molecule of N_{2} reduced. 8 protons are needed for this reduction. N_{2}& + 8 e^{-}& + 8 H^{+}& + 16 ATP → 2 NH_{3}& + H_{2}& + 16 ADP + 16 iP