Nitrogenases molybdenum, 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. 

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. 

The iron-sulfur cubes that have been detected by x-ray analysis (49) as constituents of the enzymes ferridoxin and high-potential iron protein have been extruded from these enzymes by replacing the sulf-hydryl ligands of the enzymes with simple mercaptans, and these cubes identified with the corresponding synthetic compounds, II (50, 51, 52, 53). The latter have oxidation-reduction properties that closely mimic those of the enzymes. Similarly, an iron-sulfur-molybdenum double cube has been ejected from nitrogenase, and a similar double cube has been synthesized by Holm and his collaborators (54). It remains to be seen whether or not the iron-sulfur-molybdenum double cube can mimic the properties of nitrogenase (55). 

Unlike the nitrogenases, which do not vary much in composition and physical properties with the source, nitrate reductases vary considerably from one organism to the next. The only feature which they all seem to have in common is an absolute requirement for the presence of molybdenum. 

Newton, W. E., Schultz, F. A., Gheller, S. F., Lough, S., McDonald, J. W., Conradson, S. D., Hedman, B., Hodgson, K. O. (1986), Iron-molybdenum cofactor of Azotobacter vinelandii nitrogenase oxidation-reduction properties and structural insights. Polyhedron 5, 567-72. 

Most of the current knowledge concerning the mechanism of nitrogenases is based upon extensive studies of the molybdenum nitrogenase hence this enzyme will be the focus of discussion in this article. The general properties of the molybdenum nitrogenase are described in Section 2, and the catalytic and assembly mechanism of this enzyme system will be dealt with in Sections 3 and 4. The alternative nitrogenase systems will also be briefly discussed in Section 5. 

Nitrogenase is another big target of cluster synthesis. The X-ray elucidation of the active center of the Fe-Mo cofactor and P-cluster (5) has accelerated the efforts to find rational preparative methods of trinuclear or cubane-type clusters containing molybdenum (6-9). The raft cores in these cluster complexes are one of the general structural units also in solid-state compounds, and the mutual relationships are very important. A number of review articles are now available on the syntheses, structures, and other properties of metal chalcogenide cluster compounds (6, 7,10-24). 

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