Nitrogenase catalytic mechanism

Some microbes turn nitrogen gas from the air into ammonia, making nitrogen available to living systems. The enzyme nitrogenase carries out the conversion at a small metal-containing site. What sequence of chemical steps lets it break the bond joining the two nitrogen atoms and form ammonia?[1] [3]

Nitrogen-fixing microbes convert the tightly bonded pair of atoms in nitrogen gas into ammonia. What atomic sequence makes this possible in molybdenum nitrogenase? The enzyme’s active site contains an iron–sulfur cluster with molybdenum, embedded in a protein. Electrons and protons, positively charged hydrogen nuclei, enter as the reaction proceeds.

The task is to identify the temporary bound molecules, or reaction intermediates, and the steps that weaken the nitrogen bond and release ammonia. Calculations propose possible sequences, while structures and other measurements constrain them. A structure captures a state or mixture of states, rather than following every bond change through a complete cycle.[1] [2] [3]

Detailed pathways are proposed, but experiments do not yet select every atomic step.[1] [2] [3]

The July 2026 complete-cycle proposal retains disagreement between some calculated barriers and experimental reaction rates. A separate computational study favors a particular order of hydrogen release and nitrogen binding at an intermediate state. Neither a favored calculation nor the new archaeal structures selects every step of a complete, experimentally consistent cycle.[1] [2] [3]

This conversion connects atmospheric nitrogen to the nitrogen used in living matter. Explaining its chemistry would show how an enzyme’s metal-containing structure accomplishes a transformation that nitrogen gas does not readily undergo on its own.[1] [3]

The reaction is a gateway by which atmospheric nitrogen becomes usable in living systems. It also offers a concrete test of enzyme chemistry: how a particular arrangement of metals, sulfur and surrounding protein directs a sequence of bond changes. Resolving the sequence would explain which structural features perform which chemical jobs, rather than merely showing that ammonia is produced.[1] [3]