Nitrogenase iron molybdenum cofactor

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

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. 

S-adenosylmethionine (SAM or AdoMet) superfamily, aconitase, and others), enzymes that contain Fe-S heteroatomic clusters (nitrogenase iron-molybdenum cofactor (FeMoco), carbon monoxide dehydrogenase (CODH), and acetyl CoA synthase (ACS)), and enzymes that contain unique ligation sets around specialized iron centers ([NiFe] and [FeFe] hydrogenases) (Figure 1). ... 

Biosynthesis of the Nitrogenase Iron-Molybdenum-Cofactor from Azotobacter vinelandii... 

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. 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.

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. 

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. 

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. 

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... 

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

Frank, P., Angove, H. C., Burgess, B. K., and Hodgson, K. O. (2001) Determination of ligand binding constants for the iron-molybdenum cofactor of nitrogenase monomers, multimers, and cooperative behavior, J. Biol. Inorg. Chem. 6, 683-697. 

Newton, W. E., Schultz, F. A., Gheller, S. F., Lough, S., McDonald, J. W., Conradson, S. D., Hedman, B., Hodgson, K. O. (1986), Iron-molybdenum cofactor of Azotobacter vinelandii nitrogenase oxidation-reduction properties and structural insights. Polyhedron 5, 567-72. 

Smith, B. E. Studies on the iron-molybdenum cofactor from the nitrogenase Mo-Fe protein of Klebsiella pneumoniae, in Ref. 7, p. 179... 

Enzymes containing molybdenum are of two types (1) Nitrogenases, which are required for converting atmospheric nitrogen to nitrogen compounds (NH3, for example) nitrogenases contain a characteristic polymetal atom cluster species called the iron-molybdenum cofactor, FeMoco (Section 17-E-10). (2) The other Mo enzymes, all of which have some variant of a characteristic molybdenum cofactor, Moco. 

F. Barriere, M. C. Durrant, and C. J. Pickett, Chemical Models, Theoretical Calculations, and the Reactivity of the Isolated Iron-Molybdenum Cofactor, in Catalysts for Nitrogen Fixation, Nitrogenases, Relevant Chemical Models and Commercial Processes , Nitrogen Fixation Origins, Applications, and Research Progress eds. B. E. Smith, R. L. Richards, and W. E. Newton, Kluwer Academic Publishers, The Netherlands, 2004, Vol. l,Chap.7,p. 161. 

W. E. Newton, Isolated iron-molybdenum cofactor of nitrogenase, in Biological Nitrogen Fixation , eds. G. Stacey, R. H. Burris, and H. J. Evan, Chapman HaU, New York, 1992, p. 877. 

W. E. Newton and D. R. Dean, Role of the iron-molybdenum cofactor polypeptide environment in azotobacter vinelandii-nitrogenase catalysis, in Molybdenum Enzymes, Cofactors and Model Systems , eds. E. I. Stiefel, D. Coucouvanis, and... 

CCS = copper chaperone for superoxide dismutase Moco = molybdenum cofactor MPT = molybdopterin FeMoco = iron-molybdenum cofactor of nitrogenase, SODl = Cu/Zn superoxide dismutase. 

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