Hydrazine is a product of dinitrogen reduction by the vanadium-nitrogenase from Azotobacter chroococcum.
During the enzymic reduction of N2 to NH3 by Mo-nitrogenase, free hydrazine (N2H4) is not detectable, but an enzyme-bound intermediate can be made to yield N2H4 by quenching the enzyme during turnover [Thorneley, Eady & Lowe (1978) Nature (London) 272, 557-558]. In contrast, we show here that the V-nitrogenase of Azotobacter chroococcum produces a small but significant amount of free N2H4 (up to 0.5% of the electron flux resulting in N2 reduction) as a product of the reduction of N2. The amount of N2H4 formed increased 15-fold on increasing the assay temperature from 20 degrees C to 40 degrees C. Activity cross-reactions between nitrogenase components of Mo- and V-nitrogenases showed that the formation of free N2H4 was associated with the VFe protein. These data provide the first direct evidence for an enzyme intermediate at the four-electron-reduced level during the reduction of N2 by V-nitrogenase.
Dilworth
M J
MJ
School of Biological and Environmental Sciences, Murdoch University, Western Australia.
Eady
R R
RR
D001395:Azotobacter / Q000201:enzymology*; D006834:Hydrazines / Q000032:analysis / Q000378:metabolism*; D007700:Kinetics; D008954:Models, Biological; D009584:Nitrogen / Q000378:metabolism*; D009591:Nitrogenase / Q000378:metabolism*; D013816:Thermodynamics; D014639:Vanadium
D006834:Hydrazines; D014639:Vanadium; C029424:hydrazine; D009591:Nitrogenase; D009584:Nitrogen