The mechanism for electron transfer in nitrogenase.

Nitrogenases are the only enzymes in nature that can activate the extremely inert N2 molecule. The process is termed nitrogen fixation. In Mo-nitrogenase, a complicated cofactor, termed FeMoco, with seven irons and one molybdenum, catalyzes the sequence of reactions forming ammonia. So far, most work trying to describe and understand the mechanism, has focused on the reactions at the active FeMoco site. In the present study, the interest is instead on the electron delivery to the cofactor. A previous computational study has suggested that the electrons donated must come with a very small cost of 60 kcal mol-1 or less, corresponding to a donor with a redox potential of -1.5 V. It has been known that the mechanism for electron delivery is very complicated, involving the docking of two proteins and the hydrolysis of two ATP for every electron donated. A suggestion for why that is necessary is presented here.