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Related Experiment Videos

Trapping a hydrazine reduction intermediate on the nitrogenase active site.

Brett M Barney1, Mikhail Laryukhin, Robert Y Igarashi

  • 1Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, USA.

Biochemistry
|June 1, 2005
PubMed
Summary

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Researchers trapped hydrazine, a nitrogenase substrate, at the enzyme's active site. This breakthrough advances understanding of nitrogen fixation mechanisms using advanced spectroscopy.

Area of Science:

  • Biochemistry
  • Enzymology
  • Bioinorganic Chemistry

Background:

  • Nitrogenase is crucial for biological nitrogen fixation, converting N(2) to ammonia.
  • Understanding nitrogenase mechanisms is challenging due to difficulties in trapping enzyme-substrate intermediates.
  • Previous studies suggested nitrogenous substrates bind to a specific FeS face of the FeMo-cofactor.

Purpose of the Study:

  • To develop a strategy for trapping nitrogenase-substrate adducts.
  • To characterize the trapped hydrazine-nitrogenase intermediate using spectroscopy.
  • To elucidate the binding site and mechanism of nitrogenase action.

Main Methods:

  • Site-directed mutagenesis of nitrogenase (alpha-70(Val) to alanine and alpha-195(His) to glutamine).
  • Enzyme turnover with hydrazine as substrate.

Related Experiment Videos

  • Freeze-trapping of enzyme intermediates.
  • Electron Paramagnetic Resonance (EPR) and Electron Nuclear Double Resonance (ENDOR) spectroscopy.

    • Main Results:

    • A doubly substituted MoFe protein (alpha-70(Ala)/alpha-195(Gln)) efficiently trapped a hydrazine-FeMo-cofactor adduct.
    • The trapped adduct was stabilized in a high-yield S = 1/2 state.
    • EPR spectroscopy revealed a rhombic signal (g = [2.09, 2.01, 1.93]) at optimal pH 7.4.
    • ENDOR spectroscopy with (15)N-labeled hydrazine confirmed the presence of a hydrazine-derived species bound to the FeMo-cofactor.

    Conclusions:

    • The study successfully trapped and characterized a hydrazine adduct of nitrogenase.
    • This trapped intermediate provides crucial insights into the nitrogenase mechanism.
    • The findings support the hypothesis of a common binding site for nitrogenous substrates on the FeMo-cofactor.