Nitrogenase enzymatic mechanism

Hoffman BM, Dean DR, Seefeldt LC. Climbing nitrogenase toward a mechanism of enzymatic nitrogen fixation. Acc Chem Res. 2009 42 609-19. 

The reactions of dinitrogen in its mononuclear complexes (J. Chatt, J. Organometallic Chem., 1975. 100, 17). Non-enzymatic simulation of nitrogenase reactions and the mechanism of biological nitrogen fixation (G. N. Schrauzer, Anyew. Chem. Internal. Edn.. 1975. 14. 514). 

Sulfur plays a central role in enzymatic catalysis and metal sulfido enzymes can activate various small molecules in biological conditions [20]. Much work has been devoted to the isolation and understanding of the intimate mechanisms of activation of biomimetic sulfur-containing complexes [21]. However, these systems do not present significant solubility in water under the studied conditions. We can nevertheless refer to the Sellman group s work in which the authors isolated sulfur-containing representative [FeMo] complexes of the cofactor of [FeMo] nitrogenases [22, 23], and were able to produce water-soluble complexes by introduction of... 

Nitrogenase, as must now become clear, is a complex enzyme of two component proteins which requires ATP, a reductant, a reducible substrate, Mg " " as an activator, and an anaerobic environment to function. To this complexity must be added the difficulty that the component proteins have no enzymatic half reactions . There are, perhaps, four main questions to decide about the mechanism (1) the role(s) of the two component proteins (2) the role(s) of ATP (3) the nature of the active site(s) and (4) the mechanism of N2 reduction. Despite the complexities and difficulties mentioned above, progress in the last 15 years has partly answered all these questions. The Fe protein mediates an ATP-dependent electron transfer from the donor to the MoFe protein which contains the active site. MgATP binds and induces a conformational change in the Fe protein which lowers its redox potential. FeMoco, the molybdenum cofactor, which may be part of the active site of N2 reduction, has been isolated and partly characterized, while an intermediate in N2 reduction has recently been discovered (Thorneley ct al., 1978). The next part of this chapter describes the evidence for these claims. This evidence involves the noncatalytic reactions of the individual proteins, their... 

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