Azotobacter, nitrogenase systems

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). 

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. 

Eady, R.R. 1995. Vanadium nitrogenases of Azotobacter. Metal Ions in Biological Systems 31 363 -05. 

Meanwhile we can show (50) that the deazaflavin radical generated by photodissociation of the dimer as shown in Figure 7 can be utilized for selective reduction of flavodoxin radical. With the aid of this le -transfer method Scherings, Haaker, and Veeger (51) were able to show that flavodoxin is the actual electron donor for the Azotobacter nitrogen-ase system and that N2 reduction can be maintained in the light by an artificial chain system of the reactant sequence EDTA-deazaflavin—flavodoxin—nitrogenase. Hence, Azotobacter flavodoxin is actually a carrier... 

W. E. Newton and D. R. Dean, Role of the iron-molybdenum cofactor polypeptide environment in azotobacter vinelandii-nitrogenase catalysis, in Molybdenum Enzymes, Cofactors and Model Systems , eds. E. I. Stiefel, D. Coucouvanis, and... 

Both proteins contain iron-sulfur clusters. Nitrogenase also contains a tightly bound iron-molybdenum cofactor. Some variations on this theme are known. Some bacteria, such as Azotobacter, contain more than one nitrogenase complex. Of the three systems in Azotobacter, one uses vanadium instead of molybdenum and another uses only iron. 

---