Molybdenum protein

Nitrogenase, which catalyzes the reduction of N2 to two molecules of NH3, has a different molybdenum -iron cofactor (FeMo-co). It can be obtained by acid denaturation of the very oxygen-labile iron-molybdenum protein of nitrogenase followed by extraction with d i methyl formamide.655,656 The coenzyme is a complex Fe-S-Mo cluster also containing homocitrate with a composition MoFe7S9-homocitrate (see Fig. 24-3). Nitrogenase and this coenzyme are considered further in Chapter 24. 

Xanthine hydrogenase and aldehyde dehydrogenase also give desulfo proteins which have no catalytic activity and lower redox potentials. A molybdenum protein from Desulfovibrio gigas has been isolated, which appears to have similar properties to the desulfo proteins.1011... 

A cofactor can be extracted from the iron-molybdenum protein, using Af-methylformamide. This cofactor (called FeMoCo) has many spectroscopic properties in common with the native protein, especially the EXAFS spectrum, and activates the inactive large protein derived from Azobacter vinelandii UW45 mutant which cannot incorporate molybdenum. The cofactor contains no protein or peptide, but does contain molybdenum, iron, and sulfur in atomic ratios of 1 6-8 4-9. It is believed to contain the dinitrogen-binding site (presumably molybdenum) but there is no definitive proof of this. 

Avaible experimental structural and kinetics data and energetic considerations indicate two plausible roles of ATP in the nitrogenase reduction a) the triggering of electron transfer from iron protein to iron-molybdenum protein (Howard and Rees, 1994 Rees and Howard, 2000) and the strengthening reducing power of the enzyme catalytic redox centers (Likhtenshtein and Shilov, 1977, Likhenshtein 1988a, Syrtsova and Timofeeva, 2001 see also Section 6.1.4). 

Dean, D.R., Setterquist, R.A., Brigle, K.E., Scott, D.J., Laird, N. F., Newton, W.E., (1990) Evidence that conserved residues Cys-62 and Cys-154 within the Azotobacter vinelandii nitrogenase iron-molybdenum protein a-subuflit are essential for nitrogenase activity but conserved residues His-83 and Cys-88 are not. Mol. Microbiol. 4(9),... 

A significant breakthrough has occurred in the crystallographic analysis of the iron-molybdenum protein of nitrogenase. The overall distribution of the metal clusters in the protein is shown in Eigure 7.40. The distance between the two FeMoco units is fully consistent with each cofactor acting as an independent active site. On the other hand, the closeness of the P cluster and FeMoco centers in each unit is indicative of their likely cooperation in the N2 fixation reaction. 

Iron-sulfur proteins, Fe-S-proteins, a family of proteins occurring in all organisms. They contain iron-sulfur centers (iron sulfur clusters), and can be subdivided into simple Fe-S-proteins, such as ferre-doxin, rubredoxin, and conjugated Fe-S-proteins, e.g., Fe-S-molybdenum proteins. They are included in non-heme iron proteins as the iron is not bound in a porphyrin ring system. Fe-S clusters are cofactors of numerous proteins with important... 

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