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ENDOR/HYSCORE Studies of the Common Intermediate Trapped during Nitrogenase Reduction of N2H2, CH3N2H, and N2H4 Support an Alternating Reaction Pathway for N2 Reduction.
- Source :
-
Journal of the American Chemical Society . 8/3/2011, Vol. 133 Issue 30, p11655-11664. 10p. - Publication Year :
- 2011
-
Abstract
- Enzymatic N2 reduction proceeds along a reaction pathway composed of a sequence of intermediate states generated as a dinitrogen bound to the active-site iron-molybdenum cofactor (FeMo-co) of the nitrogenase MoFe protein undergoes six steps of hydrogenation (e-/H+ delivery). There are two competing proposals for the reaction pathway, and they invoke different intermediates. In the 'Distal' (D) pathway, a single N of N2 is hydrogenated in three steps until the first NH3 is liberated, and then the remaining nitrido-N is hydrogenated three more times to yield the second NH3. In the 'Alternating' (A) pathway, the two N's instead are hydrogenated alternately, with a hydrazine-bound intermediate formed after four steps of hydrogenation and the first NH3 liberated only during the fifth step. A recent combination of X/Q-band EPR and 15N, 1,2H ENDOR measurements suggested that states trapped during turnover of the α-70Ala/α-195Gln MoFe protein with diazene or hydrazine as substrate correspond to a common intermediate (here denoted I) in which FeMo-co binds a substrate-derived [NxHy] moiety, and measurements reported here show that turnover with methyldiazene generates the same intermediate. In the present report we describe X/Q-band EPR and 14/15N, 1,2H ENDOR/HYSCORE/ESEEM measurements that characterize the N-atom(s) and proton(s) associated with this moiety. The experiments establish that turnover with N2H2, CH3N2H, and N2H4 in fact generates a common intermediate, I, and show that the N-N bond of substrate has been cleaved in I. Analysis of this finding leads us to conclude that nitrogenase reduces N2H2, CH3N2H, and N2H4 via a common A reaction pathway, and that the same is true for N2 itself, with Fe ion(s) providing the site of reaction. [ABSTRACT FROM AUTHOR]
- Subjects :
- *NITROGENASES
*IRON
*MOLYBDENUM
*HYDROGENATION
*HYDRAZINES
*NITROGEN
*PROTONS
Subjects
Details
- Language :
- English
- ISSN :
- 00027863
- Volume :
- 133
- Issue :
- 30
- Database :
- Academic Search Index
- Journal :
- Journal of the American Chemical Society
- Publication Type :
- Academic Journal
- Accession number :
- 65170113
- Full Text :
- https://doi.org/10.1021/ja2036018