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The migration of H atoms over S and Fe atoms in the reaction domain of FeMo-co, the active site of nitrogenase is described and used to explain mechanistic data on the catalyzed reductions of [N.sub.2] and [C.sub.2][H.sub.2]. The positions of H atoms influence the binding of substrates [N.sub.2] and [C.sub.2][H.sub.2] and the bound substrate blocks further migration of H atoms past the binding site.

H ENDOR data from the S(sub EPR1) intermediate formed during turnover of the nitrogenase alpha-195 (super GLN) MoFe protein with C2H2/C2D2 in H2O/D2O buffers, reexamined in context with the study of the intermediate formed from propargyl alcohol, indicate that S(EPR1) is a product complex, likely with C2H4 bound as a ferracycle to a single Fe of the FeMo-cofactor active site. It exhibits the same valencies as those of the CO-bound cofactor of the lo-CO intermediate formed during turnover.

The possibility of an exchanging N by using electron-nuclear double resonance (ENDOR) and electron spin-echo envelope modulation (ESEEM) spectroscopies is tested to examine the FeMo-co in wild-type. Nitrogenase that consists of the electron-transfer Fe protein and active-site-containing MoFe protein reduces N2 to two NH3 under atmospheric pressure and temperature in a reaction coupled to the hydrolysis of ATP.

The structural and energetic consequences of a central Logan in the femora are investigated by means of density functional calculations. It is shown that nitrogen is the only central ligand, which leads both to an energetically stable structure and to a geometry resembling the one found experimentally.