Iron molybdenum cofactor

As well as donating electrons to the MoFe protein, the Fe protein has at least two and possibly three other functions (see Section IV,C) It is involved in the biosynthesis of the iron molybdenum cofactor, FeMoco it is required for insertion of the FeMoco into the MoFe protein polypeptides and it has been implicated in the regulation of the biosynthesis of the alternative nitrogenases. 

Fig. 4. Structure of the iron molybdenum cofactor, FeMoco (after Chan, Kim, and Rees, (4) Bolin et al. (5) and Mayer et al. (7)). The FeMoco is ligated, within the a subunits of the a2j82 tetrameric structure, by residues Hisa442 and Cysa275 (Avl residue numbers).

Fig. 1. Schematic illustration of the enzyme nitrogenase being composed of the molybdenum-iron (MoFe) protein, an oc2p2 tetramer with two unique iron-sulfur clusters (P-cluster) and two iron-molybdenum cofactors (FeMoco), and the iron protein with one [4Fe-4S]-cluster and two ATP binding sites.

Actual electron transfer to the dinitrogen substrate at the MoFe-protein, with electrons first passing through the MoFe-protein s P-cluster. During this process, dinitrogen is most probably bound to the iron-molybdenum cofactor (FeMoco) of the MoFe-protein.6... 

Figure 15. Possible structures for the iron—molybdenum cofactor of nitrogenase.

K), Fe-S cluster assembly (nIfM) and the biosynthesis of the iron molybdenum cofactor, FeMo-co (nifN, B, E, Q, V, H)(5a). It is the last two functions, involving the placement of unusual transition metal sulfide clusters into the nitrogenase proteins, that cause nitrogenase and its components to be appropriately included in this symposium. 

Fig. 15. Structure of the homocitrate component of the nitrogenase iron-molybdenum cofactor.

A large number of studies devoted to metal-sulfur centers are motivated by the occurrence of such arrangements at the active site of various metalloenzymes [1-13]. Mononuclear complexes with Mo=0 func-tion(s) and possessing sulfur ligands in their coordination sphere have been extensively investigated since they can be seen as models of the active site of enzymes such as nitrate- and DM SO reductases or sulfite- and xanthine oxidases [1-4]. On the other hand, a large variety of mono-, di-, and polynuclear Mo—S centers have been synthesized in order to produce functional models of the Mo-nitrogenase since the exact nature (mono-, di- or polynuclear) of the metal center, where N2 interacts within the iron-molybdenum cofactor (FeMo—co) of the enzyme is still unknown [4-8]. 

A large part of the research involving metal-sulfur complexes (metal = molybdenum or iron) is aimed at designing functional models of the active site of nitrogenase, the iron-molybdenum cofactor, EeMo—CO [4-8, 12, 13]. Only a very... 

More complex iron-sulfur clusters are also known to exist. These include the iron-molybdenum cofactor of nitrogenase (Thornely and Lowe, 1984) and probably larger clusters in which the only metal is iron (Hagen, 1987). They are characterized by highly anisotropic EPR spectra from S > ground states the nitrogenase cluster, for example is S = j and has EPR features near g = 4 and g = 2. 

PDB ID 1 N2C) (a) In this ribbon diagram, the dinitrogenase subunits are shown in gray and pink, the dinitrogenase reductase subunits in blue and green. The bound ADP is red. Note the 4Fe-4S complex (Fe atoms orange, S atoms yellow) and the iron-molybdenum cofactor (Mo... 

One of the enzymes given in Table 23 is nitrogenase, which is responsible for the fixation of dinitrogen to give ammonia. Molybdenum probably serves as the binding site for N2, and is present in the iron-molybdenum cofactor, which is a molybdenum-iron sulfide cluster. Nitrogenase will be considered in Section 63.1.14, which deals with the nitrogen cycle. 

X-ray crystallography has revealed that each a2p2 tetrameric MoFe protein contains two each of two types of cluster [13-16], These are the iron molybdenum cofactor (FeMoco) centers and the Fe8S7 P clusters. The two FeMoco centers are bound within the a subunits about 1 nm below the surface of the protein and are separated by about 7 nm. The P clusters are situated at the interface of the a and P subunits, and each is approximately 1.9 nm from one of the FeMoco centers. 

The most efficient system of this type is obtained by the reduction of bovine serum albumin in the presence of molybdate. Apparently disulfide links in the peptide are broken and form thiolate groups which then bind molybdenum. In a borate buffer, this system will reduce dinitrogen and acetylene, although not using dithionite as an electron source. The turnover is similar to that of the iron-molybdenum cofactor (see Section XII), and dinitrogen reduction is inhibited by carbon monoxide and stimulated by ATP. The yield of ammonia is linearly dependent upon PN2, and the yield is also depressed in the presence of fumarate and, more surprisingly, succinate. It is calculated that the... 

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... 

Lancaster KM, Roemelt M, Ettenhuber P, et al. X-ray emission spectroscopy evidences a central carbon in the nitrogenase iron-molybdenum cofactor. Science. 2011 334 974-7. 

Durrant, M.C. (2001) Controlled protonation of iron-molybdenum cofactor by nitrogenase a structural and theoretical analysis, Biochem. J. 355, 871-891. 

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