Kinetic studies of the nitrogenase-catalyzed hydrogen evolution and nitrogen reduction reactions

The mechanism of Klebsiella pneumoniae nitrogenase action. Pre-steady-state kinetics of an enzyme-bound intermediate in N2 reduction and of NH3 formation

“…This supports the suggestion by Chatt (1980) that N2 binds to Kplt by the displacement of H2 and that the inhibition by H2 of NH3 formation is a massaction effect on this equilibrium. In Scheme 3, this occurs at species E3 and E4 in order to explain the results reported by Silverstein & Bulen (1970) and , which showed that the relative steady-state rates of H2 and NH3 formation depended on the electron flux through the MoFe protein. NH3 formation…”

Evidence for a Two-Electron Transfer Using the All-Ferrous Fe Protein during Nitrogenase Catalysis

“…For example, using 5-7 mM Ti(III) as reductant, nitrogenase is active and the ATP utilization per electron pair transferred (ATP/2e) decreases from 4 -5, typically observed with DT, to values near 2 (10,11 (6,12), MoFe inhibition (6,12), the dilution effect (13)(14)(15)(16), the delay in product formation (the lag phase) at high MoFe:Fe protein ratios (17,18), and inhibition due to Av-Cp heterologous cross reactions (19 -21) ), and used for the experiments described below (11).…”

Nitrogenase and nitrogenase reductase associate and dissociate with each catalytic cycle.

“…The larger *protein (molecular weight 210,000-242,000) contains Mo, Fe, and acid-labile sulfur, whereas the smaller protein (molecular weight 55,000-66,000) contains Fe and acid-labile sulfur. Because neither protein alone exhibits any catalytic activity, they frequently are described as forming a catalytically competent complex (2)(3)(4). An alternative explanation of the behavior of the two proteins is that the smaller protein serves as a specific reductase for the larger protein, and that the larger protein then reduces N2 or other substrates.…”