Iron-molybdenum cofactor, FeMoco synthesis

The conversion of dinitrogen to ammonia is one of the important processes of chemistry. Whereas the technical ammonia synthesis requires high temperature and pressure (1), this reaction proceeds at room temperature and ambient pressure in nature, mediated by the enzyme nitrogenase (2). There is evidence that N2 is bound and reduced at the iron-molybdenum cofactor (FeMoco), a unique Fe/Mo/S cluster present in the MoFe protein of nitrogenase. Although detailed structural information on nitrogenase has been available for some time (3), the mechanism of N2 reduction by this enzyme is still unclear at the molecular level. Nevertheless, it is possible to bind and reduce dinitrogen at simple mono- and binuclear transition-metal systems which allow to obtain mechanistic information on elemental steps involved... 

The iron-molybdenum cofactor ( FeMoco or M cluster ) is widely accepted to be the site of N2 binding and reduction. Mutations near this site, or the absence of homocitrate (from nifV mutants) greatly affect the catalytic specificity and activity. The enzyme is inactive if the biosynthetic machinery for FeMoco synthesis is removed, but becomes active if extracted FeMoco (see Section 8.22.2.3.4) is added. The characteristic EPR signal for the FeMoco changes under turnover conditions, and, as shown below, some substrates have been shown to bind at the FeMoco. 

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