Nitrogenases properties

Molybdenum nitrogenase has been the subject of intensive study for more than 30 years, but much less work has been done on the vanadium and iron-only nitrogenases. Consequently, we first review the properties of Mo nitrogenase, and then in later sections outline what is known of the other two enzymes. 

Four distinct types of Fe-S center have now been found in proteins, ranging from mono- to tetranuclear in addition, a novel Mo-Fe-S cluster is present in the enzyme nitrogenase. Synthetic analogs of most of these have been prepared and used to provide insight into the intrinsic properties of the metal-sulfur centers in the absence of protein-imposed constraints. The strategies used to prepare both Fe-S and Mo-Fe-S clusters are described they range from spontaneous self-assembly to the designed synthesis of clusters with specific structural features. 

D = -0.7 cm", E/D = 0.26 for the S = 3/2 center in dithionite-reduced AvV (B. J. Hales, unpublished results). MCD magnetization data for dithionite-reduced Avl and Avl (8) indicate that the EPR-detectable S = 3/2 paramagnets are also responsible for the temperature-dependent MCD transitions. Therefore, by analogy with the MoFe protein it seems probable that the S = 3/2 paramagnetic chromophore in dithionite-reduced Avl is a V-Fe-S cluster. However, the EPR and MCD studies indicate that this cluster has magnetic and electronic properties distinct from that of the Mo-Fe-S clusters in conventional Mo nitrogenases. 

Mo-independent nitrogenases, 36 83-84 nitrogen fixation, 36 81-84 physicochemical properties, 36 82 Fepr protein, 47 245-247 crystallography, 47 232-233 from Desulfovibrio desulfuricans, 47 227-228, 229, 232... 

Although the hypothesis of Egumi may be an oversimplification, it is certainly true that Fe /Feu is widely used in redox systems. Zn " in hydrolysis, esterification, and similar reactions, and molybdenum in nitrogenase. xanthine oxkkise. nitnite reductase, etc Putting abundance aside, discuss the specific chemical properties of these metals this make them well suited for their tasks. 

Recently we have attempted to pursue multi-electron fixation processes as models for N2 or CO2 fixation. In nature, the N2-fixation enzyme, nitrogenase, exhibits non-specificity properties, and acetylene competes for nitrogen as the fixation substrate (21). The fixation process of acetylene to methane and of nitrogen to ammonia (euqations 14 and 15) have several common features (i) both involve the cleavage of a triple bond (ii) the two reactions involve 6 electrons in the fixation mechanism. Thus, it seems that the photocleavage of acetylene to methane might offer a good model for development of -fixation cycles (22). 

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