Intermediates trapped during nitrogenase reduction of N triple bond N, CH3-N=NH, and H2N-NH2.
A high population intermediate has been trapped on the nitrogenase active site FeMo cofactor during reduction of N2. In addition, intermediates have been trapped during reduction of CH3-N=NH by the alpha-195Gln variant and during reduction of H2N-NH2 by the alpha-70Ala/alpha-195Gln variant. Each of these trapped states shows an EPR signal arising from an S = 1/2 state of the FeMo cofactor. 15N ENDOR shows that each intermediate has a nitrogenous species bound to the FeMo cofactor, with a single type of N seen for each bound intermediate. The g tensors are unique to each intermediate, g(e) = [2.084, 1.993, 1.969], g(m) = [2.083, 2.021, 1.993], g(l) = [2.082, 2.015, 1.987], as are the 15N hyperfine couplings at g1, which suggests that three distinct stages of NN reduction may have been trapped. The 1H ENDOR spectra show that the N2 intermediate is at a distinct and earlier stage of reduction from the other two, so at least two stages of NN reduction have been trapped. Some possible structures of the hydrazine intermediate are presented.
Barney
Brett M
BM
Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, USA.
Yang
Tran-Chin
TC
Igarashi
Robert Y
RY
Dos Santos
Patricia C
PC
Laryukhin
Mikhail
M
Lee
Hong-In
HI
Hoffman
Brian M
BM
Dean
Dennis R
DR
Seefeldt
Lance C
LC
D000577:Amides / Q000737:chemistry*; D000588:Amines / Q000737:chemistry*; D001665:Binding Sites; D020134:Catalytic Domain; D004578:Electron Spin Resonance Spectroscopy; D008983:Molybdoferredoxin / Q000737:chemistry / Q000378:metabolism*; D009584:Nitrogen / Q000737:chemistry*; D009591:Nitrogenase / Q000378:metabolism*; D010084:Oxidation-Reduction
D000577:Amides; D000588:Amines; D008983:Molybdoferredoxin; D009591:Nitrogenase; D009584:Nitrogen