Nitrogenase, nitrogen reduction

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... 

Nitrogen reduction Nitrogenase has been a model system for studying general principles involving electron... 

It also seems to be noteworthy that in the presence of phospholipids the nitrogen reduction catalyzed by an artificial nitrogenase system is very selectively enhanced [45], Ding et al. [46] gave examples of the use of chiral amphiphilic ligands in hydrogenation reactions but directed attention to their application in biphasic systems. Usually, the presence of water causes loss of activity and, in the case of enantioselective hydrogenation, loss of enantioselectivity [47]. 

Figure 4. Proposed mechanism for nitrogen reduction at a molybdenum site in nitrogenase. 1980, used with permission of the American Chemical Society [10].

There are several other references on the chemistry of nitrogen reduction in model complexes and on the biochemistry with nitrogenases. 

These enzymes are somewhat less active toward N2 than the molybdenum-dependent nitrogenase. However, recall that (i) protein dissociation is usually rate limiting, and (ii) proton reduction competes with nitrogen reduction. Therefore, it is likely that the activation barriers are similar for nitrogen reduction by the different nitrogenases. There is high sequence homology (and invariably... 

The reaction proceeds with co-evolution of hydrogen. Nitrogenase has been studied extensively and appears to contain three different kinds of Fe/Mo/S clusters distributed over two proteins. The actual nitrogen reduction takes place at the FeyMoSs cluster shown in Fig. 7.15. 

A number of nitrogen-fixing bacteria contain vanadium and it has been shown that in one of these, Azotobacter, there are three distinct nitrogenase systems based in turn on Mo, V and Fe, each of which has an underlying functional and structural similarity.This discovery has prompted a search for models and the brown compound [Na(thf)]+[V(N2)2(dppe)2] (dppe = Pli2PCH2CH2PPh2) has recently been prepared by reduction of VCI3 by sodium naphthalenide... 

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