Molybdenum cofactors

Molybdenum, tris(phenylenedithio)-structure, 1,63 Molybdenum alkoxides physical properties, 2,346 synthesis, 2,339 Molybdenum blue liquid-liquid extraction, 1,548 Molybdenum cofactor, 6,657 Molybdenum complexes acrylonitrile, 2,263 alkoxides, 3,1307 alkoxy carbonyl reactions, 2,355 alkyl, 3,1307 alkyl alkoxy reactions, 2,358 alkyl peroxides oxidation catalyses, 6,342 allyl, 3,1306... 

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).

The molybdenum cofactor was liberated from D. gigas AOR, and under appropriate conditions was transferred quantitatively to nitrate reductase in extracts of Neurospora crassa nit-1 mutant) to yield active nitrate reductase 217). On the basis of molybdenum content, the activity observed for reconstitution with molybdenum cofactor of D. gigas was lower (25%) than the values observed for the procedure using extractable molybdenum cofactor of XO, used as reference. This result can now be put in the context of the difference in pterin present (MPT-XO and MCD-AOR) 218). 

They have a molecular mass of 300-360 kDa, and contain per molecule, eight atoms of Fe, eight atoms of acid-labile S, two atoms of Mo, and two molecules of FAD. The organic component of the pterin molybdenum cofactor is generally molybdopterin cytosine dinucleotide (Hetterich et al. 1991 Schach et al. 1995). 

Deficiency of molybdenum cofactor can lead to sulphite oxidase deficiency (Anke and Glei 1994). 

Fig. 5.10. The formula of one of the mononuclear molybdenum cofactors, Moco. Others have a nucleotide phosphate extension (see references to these elements in Further Reading). In sulfide-rich environments, tungsten replaced molybdenum. In some coenzymes, two pterins are bound to the metal ions.

Kisker, C., Schindelin, H. and Rees, D.C. (1997). Molybdenum cofactor - containing enzymes structure and mechanisms. Annu. Rev. of Biochem., 66, 233-267... 

The earlier switch of the molybdenum cofactor from carboxylate to sulfate and nitrate reduction. 

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 3.10 Biosynthesis of eukaryotic molybdenum cofactor occurs in four steps. (Adapted from Mendel and Bittner, 2006. Copyright 2006, with permission from Elsevier.)...

The molybdenum cofactor (Moco) is the essential component of a group of redox enzymes [20-22], which are diverse not only in terms of their phylogenetic distri-... 

Kisker, C., Sghindelin, H., Baas, D., Retey, j., Megkenstogk, R. U., and Kroneck, P. M. a structural comparison of molybdenum cofactor-containing enzymes, FEMS Microbiol Rev 1998, 22, 503-521. 

---