Nitrogenase Systems

MoFe Protein Molecular Weight and Quaternary Structure 

Puriflcation of Nitrogenase Proteins from Various Sources 

Azotobacter vinelandii French pressure cell Protamine sulfate Heat DEAE-cellulose Crystallization Prep electrophoresis 

Azotobacter chroococcum French pressure cell DEAE-cellulose Sephadex 

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The nitrogenase system reduces hundreds of millions of kilograms of nitrogen gas to ammonia each year, catalysing tire reaction at ambient temperatures and atmospheric pressure. Nitrogenase consists of two proteins tliat contain... 

A number of nitrogen-fixing bacteria contain vanadium and it has been shown that in one of these, Azotobacter, there are three distinct nitrogenase systems based in turn on Mo, V and Fe, each of which has an underlying functional and structural similarity.This discovery has prompted a search for models and the brown compound [Na(thf)]+[V(N2)2(dppe)2] (dppe = Pli2PCH2CH2PPh2) has recently been prepared by reduction of VCI3 by sodium naphthalenide... 

Fig. 12. The nitrogen fixation genes of Azotobacter vinelandii. This orgEinism has three nitrogenase systems, viz nif, vnf, and anf, which it uses for fixing N2 under different environmental conditions. The boxes with slanted hatching indicate the structural genes of the three systems, those colored dark gray are required for eiU three systems, and those with vertical hatching are required for both the vnf and anf systems.

For the sake of completeness, it is worth noting the role of vanadium in the synthesis of alternative nitrogenase systems by several aerobic bacteria, particularly those within the genus Azotobacter (Fallik et al. 1991) low yields of hydrazine are produced, and this suggests a different affinity of the nitrogenase for the N2 substrate (Dilworth and Eady 1991). 

PHOTOBIOLOGICAL HYDROGEN PRODUCTION BY CYANOBACTERIA UTILIZING NITROGENASE SYSTEMS -PRESENT STATUS AND FUTURE DEVELOPMENT-... 

In their 1960 paper, Carnahan et al. reported that ATP was inhibitory to nitrogenase activity in their cell-free preparations. Hence, when McNary and Burris [24] reported that ATP was needed to support fixation, the report was met with a good deal of skepticism. But experiments in a number of other laboratories verified the absolute need for ATP. Not only is ATP needed, it is needed in substantial amounts. Under ideal conditions 16 ATP are required per N2 reduced to 2 NH3. Under normal conditions in nature the requirement probably is in the 20 to 30 ATP per N2 range. N2 reduction is energy demanding whether it is accomplished chemically in the Haber process or enzymatically by the nitrogenase system. 

Kamen, M.D., Gest, H. 1949. Evidence for a nitrogenase system in the photosynthetic bacterium Rhodospirilliim rubum. Science 109 560. 

Masukawa, H., Mochimaru, M., Sakurai, H. 2002. Hydrogenases and photobiological hydrogen produetion utilizing nitrogenase system in cyanobaeteria. Int J Hydrogen Energy 27 1471-1474. 

The Mo-, V-, and Fe-Based Nitrogenase Systems of Azobacter Robert R. Eady... 

Since ADP is inhibitory to the nitrogenase system, it is best in laboratory studies to supply ATP from an ATP-generating system such as a mixture of creatine phosphate, creatine kinase, and a small amount of ADP (Eqs. 6-65,... 

Bulen, W.A. and LeComt, J.R. (1966) The nitrogenase system from Azotobacter two-enzyme requirement for N2 reduction, ATP-dependent H2 evolution and ATP hydrolysis, Proc. Natl. Acad. Sci. 56, 979-986. 

Fig. 4. Summary of the known oxidation states and magnetic properties of the metal-sulfur centers of the nitrogenase system. The numbers in parentheses indicate the presumed overall charge on the Fe4S4 core...

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. 

Figure 12 Assembly of the molybdenum nitrogenase. Pathways of FeMo cofactor biosynthesis, Fe protein maturation, and MoFe protein assembly are indicated in dotted, dashed, and solid arrows, respectively. The nif gene products that are also required for the vanadium and iron-only nitrogenase systems are indicated by ...

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