title: Hydrogen burst associated with nitrogenase-catalyzed reactions.
abstract: We have used a membrane-leak mass spectrometer to follow the time courses of H2 evolution and substrate reduction by nitrogenase [reduced ferredoxin:dinitrogen oxidoreductase (ATP-hydrolyzing), EC 1.18.6.1]. In the absence of added substrates, dinitrogenase passes all of its electrons to protons to form H2, but when a reducible substrate is added the electrons from dinitrogenase are shared between protons and the added substrate so that the steady-state rate of H2 production is decreased. If a reducible substrate is added before the nitrogenase reaction is initiated, a pre-steady-state burst of H2 is evident upon initiation of the reaction. This burst is associated with all the substrates of nitrogenase examined--i.e., N2, N2O, C2H2, NaN3, and NaCN. The H2 burst is stoichiometric with dinitrogenase, but not with dinitrogenase reductase. In the H2 burst phase, 1 H2 is evolved per dinitrogenase molybdenum. Although a change in the ratio of nitrogenase components changed the initial rate of the H2 burst, the stoichiometry was not affected. Production of H2 by the burst in the presence of a high concentration of substrate is terminated after production of 1 H2 per dinitrogenase molybdenum, and a steady-state rate of H2 production is established. This response suggests that the H2 burst is not a catalytic event but a result of a once-only activation process.
authors.affiliation: Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin-Madison 53706.
authors.forename: J
authors.initials: J
authors.lastname: Liang
authors.forename: R H
authors.initials: RH
authors.lastname: Burris
mesh_terms: D006859:Hydrogen; D013058:Mass Spectrometry; D008982:Molybdenum; D009591:Nitrogenase / Q000378:metabolism*; D013997:Time Factors
chemical_list: D006859:Hydrogen; D008982:Molybdenum; D009591:Nitrogenase