Open AccessHydrogen burst associated with nitrogenase-catalyzed reactions.
Author(s) -
Jiaqi Liang,
R. H. Burris
Publication year - 1988
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.85.24.9446
Subject(s) - nitrogenase , substrate (aquarium) , catalysis , chemistry , stoichiometry , molybdenum , photochemistry , inorganic chemistry , biochemistry , nitrogen , nitrogen fixation , biology , organic chemistry , ecology
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.