MoFe proteins nitrogen fixation

For further details about the progress in the syntheses of the structural models of the clusters in MoFe protein, please see the other recent reviews,33 together with those dealing with the reactions of metal-sulfur clusters relating to the nitrogen-fixation chemistry.34... 

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... 

Fisher, K., Hare, N. D., and Newton W. E. (1998), Mapping the catalytic surface of A. vinelandii MoFe protein by site specific mutagenesis, Curr. Plant Sci. Biotechnol. Agric. 31 (Biological Nitrogen Fixation for the 21st Century), 23-26. 

Figure 24.2. Nitrogen Fixation. Electrons flow from ferredoxin to the reductase (iron protein, or Fe protein) to nitrogenase (molybdenum-iron protein, or MoFe protein) to reduce nitrogen to ammonia. ATP hydrolysis within the reductase drives conformational changes necessary for the efficient transfer of electrons.

Molybdenum has long been known to have a role in nitrogen fixation over 50 years ago Bortels showed that Mo stimulated the N2-dependent growth of Azotobacter (2). Subsequently, these observations were rationalized when all purified nitrogenases were shown to be separable into an Fe protein and a MoFe protein that contained Mo as part of an essential iron- and molybdenum-containing cofactor (Fe-Moco), the probable site at which N2 is reduced. 

Nitrogen fixation occurs only in certain prokaryotes and is catalyzed by the nitrogenases, which have two protein components. These are the Fe-protein, which acts as a specific reductant of the larger MoFe-... 

In 1930, Hermann Bortels (1902-1979) recognised that nitrogen fixation is a molybdenum-dependent process. Obviously, the nitrogenases from Rhizobium meliloti, Azotobacter vinelandii and Clostridium pasteurianum have a similar constitution. In 1966, Leonard E. Mortenson identified for the first time an Fe- and a MoFe-protein as parts of the nitrogenase enzyme system. The exact structure of the nitrogenase-molybdenum-iron protein from Azotobacter vinelandii [28] was clarified in 1992, and that from Clostridium pasteurianum [29] in 1993, both by Douglas C. Rees. [30] The Fe-protein is a y2-dimer with a molar mass of some 60,000 Daltons, and the MoFe-protein is an ca. 

---