Nitrogenase metalloenzymes

Nitrogenase, Metalloenzymes, Inorganic Molecular Biology and Biomineralization... 

Nitrogenase Metalloenzyme that breaks the stable triple bond of N (nitrogen) to make the more chemically available NHj (ammonia) molecule, a process known as nitrogen fixation. ... 

On the other hand, such approaches to the metalloenzymes described above in Figures 1 and 2 are still under way. Thus, the model clusters reproducing precisely their complex metal-sulfur assemblies in the native form have not yet been isolated. In this section, the studies aiming at the syntheses of the model compounds of two clusters in nitrogenase, FeMo cofactor and P-cluster, will be surveyed. The choice of these clusters as the representatives of the metal-sulfur clusters in metalloenzymes arises from the fact that these are the largest and most complicated metal-sulfur clusters known at present among those observed in natural enzymes. 

Using protons from water (and an energy input) for reaction with metal-coordinated dinitrogen (the metalloenzyme nitrogenase)... 

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]. 

Previously unrecognized atom - possibly nitrogen -in MoFe protein of metalloenzyme nitrogenase First noble gas-actinide complexes... 

Molybdenum is required in the diet. It is required by three enzymes in mammals sulfite oxidase, xanthine dehydrogenase, and aldehyde oxidase. Molybdenum occurs in these enz)anes as part of the molybdenum cofactor (Figure 10.52). This cofactor is biosynthesized in the body with GTP as the starting material. AH known Mo metalloenzymes, with the exception of nitrogenase (a plant enz5une), use Mo in the form of the molybdemun cofactor. 

Transition-metal/sulfide sites, especially those containing iron, are present in all forms of life and are found at the active centers of a wide variety of redox and catalytic proteins. These proteins include simple soluble electron-transfer agents (the ferredoxins), membrane-bound components of electron-transfer chains, and some of the most complex metalloenzymes, such as nitrogenase, hydrogenase, and xanthine oxidase. 

In this chapter we hrst review the chemistry of the Fe-S sites that occur in relatively simple rubredoxins and ferredoxins, and make note of the ubiquity of these sites in other metalloenzymes. We use these relatively simple systems to show the usefulness of spectroscopy and model-system studies for deducing bioinorganic structure and reactivity. We then direct our attention to the hydrogenase and nitrogenase enzyme systems, both of which use transition-metal-sulfur clusters to activate and evolve molecular hydrogen. 

See also Component I, Metalloenzymes, Nitrogenase, Nitrogen Fixation, Figure 20.2, Ferredoxin, Nitrogen Fixation, Nitrogenase... 

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