Solvent Deuterium Isotope Effects of Substrate Reduction by Nitrogenase from .

The mechanism of nitrogenase, the enzyme responsible for biological nitrogen fixation, has been of great interest for understanding the catalytic strategy utilized to reduce dinitrogen to ammonia under ambient temperatures and pressures. The reduction mechanism of nitrogenase is generally envisioned as involving multiple cycles of electron and proton transfers, with the known substrates requiring at least two cycles. Solvent kinetic isotope effect experiments, in which changes of reaction rates or product distribution are measured upon enrichment of solvent with heavy atom isotopes, have been valuable for deciphering the mechanism of complex enzymatic reactions involving proton or hydrogen transfer.