FeMo-cofactor resting states

It is still debated if the overall oxidation state of the FeMo cofactor in its resting state (or, without substrate binding) has to be described as... 

ENDOR Studies on the Resting State of Nitrogenase FeMo-cofactor... 

CW 35 GHz ENDOR, of the individual Fe sites in the CO-inhibited forms,much as had been done earlier for resting state FeMo-cofactor. " Hyperfine coupling constants were determined for four Fe sites in the lo-CO and three in the high-CO forms. The signs and magnitudes of the Ajj, Fe values, in comparison with those of other FeS proteins and with extensive computational studies, allowed a proposal as to the formal oxidation state assignments of the metal ions in the FeMo-cofactor as [Fe7S9Mo]+ = [(Fe +)2, Fes +, 89 , Mo" +]+, where (Fe +)2 is the delocalized Fe Fe pair. ... 

From a biochemical point of view, the summation of the ENDOR studies on nitrogenase FeMo-cofactor interacting with carbon-containing small molecules is an electron inventory of the resting state, lo-CO form, and ethyne-bound form (Sepri), resulting in the proposal that the resting state is two electrons more oxidized than the substrate/inhibitor-bound forms and further, that these forms could be placed into the context of the Lowe-Thomeley scheme of nitrogen fixation. 

We should also mention a very surprising redox potential result for the complicated active site of the FeMo cofactor of nitrogenase having a MoFe7S9 type core. " " Here our DFT (BP86) calculations for the Mox resting state redox potential give a value much more positive than... 

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