P-Clusters of Nitrogenase

Consequently, the p /pox transition apparently involves one or the other of the two redox couples in Fig. 14. 

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Figure 2.10 Schematic structures of (a) sulfite reductase of Escherichia coli in which a 4Fe-4S cluster is linked via a cysteine to the iron in a sirohaem (b) P cluster of nitrogenase (c) FeMoCo cluster of nitrogenase (d) the binuclear site in Desulforibrio gigas hydrogenase.

Figure 3.11 (a) and (b) the P-cluster of nitrogenase in its reduced and oxidized state and (c) the FeMo-cofactor. The molecules are represented with C green, N blue, O red, S yellow, Fe orange and Mo pink. (From Voet and Voet, 2004. Reproduced with permission from John Wiley Sons., Inc.)... 

The P clusters of nitrogenase. The enzyme nitrogenase consists of two proteins the Fe protein (m.w. 55,000), which contains a single 4Fe-4S center, and the more complex MoFe protein (m.w. 220,000) (48,49). The minimum functional unit of the latter appears to be the half molecule, an asymmetric dimer containing 1 Mo, 14-16 Fe, and 16-18 sulfides. Application of a vast array of spectroscopic methods to the MoFe protein in a variety of oxidation states has led to the conclusion that it contains two types of metal-sulfur cluster in a 2 1 ratio unusual Fe S units termed P clusters, and the protein-bound form of the FeMo-cofactor (50). 

Fig. 3 Known structures of the P cluster of nitrogenase in two oxidation states.

Surerus, K. K. Hendrich, M. P. Christie, P. D. Rottgardt, D. Orme-Johnson, W. H. Miinck, E. Mossbauer and integer-spin EPR of the oxidized P-clusters of nitrogenase POX is a non-Kramers system with a nearly degenerate ground doublet. J. Am. Chem. Soc. 1992, 114(22), 8579-8590. 

FIGURE 4.6 A selective gallery of more complex organic cofactors which are found in metalloproteins. (a) The Moco cofactor (b) the FeMo-cofactor, (c) the P-cluster of nitrogenase, (d) the H-cluster of microbial hydrogenases, and (e) the Cuz cluster of microbial nitrous oxidases. 

P-cluster of nitrogenases, the three types of metal clusters found in microbial hydrogenases, the unusual common structural features of which include CO ligands, and the Cuz cluster of microbial nitrous oxidases. The biosynthesis of some of these cofactors is discussed later in this chapter. 

III) the P-clusters of nitrogenase, which may represent a variation of the [4 Fe—4 S] basic structure using different oxidation states and/or different ligation 6 F88) ... 

Nitrogenase is a multicomponent metalloenzyme that catalyzes the conversion of atmospheric dinitrogen to ammonia. For decades, it has been generally believed that the [8Fe-7S] P-cluster of nitrogenase component 1 is indispensable for nitrogenase activity. However, Hu et al identified two cataly-tically active P-cluster variants by ESR spectroscopic studies, and found that both P-cluster variants resemble [4Fe-4S]-like centers based on XAS experiments. 

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