Iron-molybdenum cofactor, FeMoco electron reduction

The enzyme system responsible for N2 reduction, called the nitrogenase complex, consists of two separate proteins. As outlined in Figure 20.4, one protein-called component I, nitrogenase, or molybdenumiron protein-catalyzes the reduction of N2, and the other-called component II, nitrogenase reductase, or iron protein-transfers electrons from ferredoxin or flavodoxin to component I. Both component I and component II contain Fe4S4 iron-sulfur clusters, and component I also contains molybdenum, in the form of a tightly bound iron-molybdenum cofactor (FeMoCo). 

In this section DFT treatments of the iron-molybdenum cofactor and the activation, reduction and protonation of N2 proceeding at this cluster are presented. The earliest of these calculations appeared after publication of the first crystal structures of nitrogenase, and this was well before the discovery of the central atom X. After the discovery of X and its identification as carbon these treatments were, in part, updated. Here we will focus both on the basic theoretical methods to treat the electronic structure of the FeMoco and the reduction of N2 mediated by this cluster. 

Nitrogen Fixation in Nature The nitrogenase enzyme is a two-component protein that consists of an electron-transfer Fe protein and a catalytic protein [85]. Three different nitrogenase enzymes are known, which differ primarily in the nature of the putative active site within the catalytic protein. The most common form is the MoFe protein, in which the active site for nitrogen reduction, the so-called FeMo cofactor (FeMoco), is composed of seven irons, one molybdenum, and nine sulfides... 

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