PMID:24062462

Citation	Duval, S, Danyal, K, Shaw, S, Lytle, AK, Dean, DR, Hoffman, BM, Antony, E and Seefeldt, LC (2013) Electron transfer precedes ATP hydrolysis during nitrogenase catalysis. Proc. Natl. Acad. Sci. U.S.A. 110:16414-9
Abstract	The biological reduction of N2 to NH3 catalyzed by Mo-dependent nitrogenase requires at least eight rounds of a complex cycle of events associated with ATP-driven electron transfer (ET) from the Fe protein to the catalytic MoFe protein, with each ET coupled to the hydrolysis of two ATP molecules. Although steps within this cycle have been studied for decades, the nature of the coupling between ATP hydrolysis and ET, in particular the order of ET and ATP hydrolysis, has been elusive. Here, we have measured first-order rate constants for each key step in the reaction sequence, including direct measurement of the ATP hydrolysis rate constant: kATP = 70 s(-1), 25 °C. Comparison of the rate constants establishes that the reaction sequence involves four sequential steps: (i) conformationally gated ET (kET = 140 s(-1), 25 °C), (ii) ATP hydrolysis (kATP = 70 s(-1), 25 °C), (iii) Phosphate release (kPi = 16 s(-1), 25 °C), and (iv) Fe protein dissociation from the MoFe protein (kdiss = 6 s(-1), 25 °C). These findings allow completion of the thermodynamic cycle undergone by the Fe protein, showing that the energy of ATP binding and protein-protein association drive ET, with subsequent ATP hydrolysis and Pi release causing dissociation of the complex between the Fe(ox)(ADP)2 protein and the reduced MoFe protein.
Links	PubMed PMC3799366 Online version:10.1073/pnas.1311218110
Keywords	Adenosine Triphosphate/metabolism; Azotobacter vinelandii/metabolism; Electron Transport/physiology; Hydrolysis; Kinetics; Models, Biological; Nitrogen Fixation/physiology; Oxidoreductases/metabolism; Spectrophotometry; Thermodynamics
edit table

Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
BRADU:NIFH	Contributes to	GO:0016163: nitrogenase activity	ECO:0000314:		F		Catalysis of the reaction 8 reduced ferredoxin + H+ + nitrogen +16 ATP = 8 oxidized ferredoxin + 2 NH3 + 16 ADP + 16	complete CACAO 10558

References

See Help:References for how to manage references in GONUTS.