The interstitial atom of the nitrogenase FeMo-Cofactor: ENDOR and ESEEM evidence that it is not a nitrogen
ABSTRACT X-ray crystallographic study of the nitrogenase MoFe protein revealed electron density from an atom (denoted X) inside the active-site metal cluster, the [MoFe7S9:homocitrate] FeMo-cofactor. The electron density associated with X is consistent with a single N, O, or C atom. We now have tested whether X is an N or not by comparing the Q-band ENDOR and ESEEM signals from resting-state (S = 3/2) MoFe protein and NMF-extracted FeMo-co from bacteria grown with either 14N or 15N as the exclusive N source. All of the 14N or 15N signals associated with the protein are lost upon extraction of the FeMo-co. We interpret this as strong evidence that X is not an N.
Chemical Reviews 01/2014; 114(8). DOI:10.1021/cr400641x · 45.66 Impact Factor
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ABSTRACT: The enzyme nitrogenase catalyzes the six-electron reduction of molecular dinitrogen to ammonium, concomitant with the reduction of protons to yield hydrogen gas. In the MoFe protein component of the nitrogenase system, the unique FeMo cofactor is the active site of catalysis, but its exact mechanism remains under debate. This review focuses on the history of the structure determination of FeMo cofactor, a process that extended over two decades and involved several iterations and corrections that are unusual and unexpected within the established field of X-ray crystallography. However, FeMo cofactor has defied expectations on several occasions, and besides being the largest single iron-sulfur cluster known to bioinorganic chemistry, this [Mo:7Fe:9S:C]:homocitrate moiety is unique in some aspects that have misled researchers several times. We have now arrived at a final and complete description of the atomic structure of FeMo cofactor, and yet many questions regarding various aspects of the catalytic mechanism of this enzyme remain to be answered.European Journal of Biochemistry 02/2014; 19(6). DOI:10.1007/s00775-014-1116-7 · 3.16 Impact Factor
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ABSTRACT: Trinuclear M3tdt3(PEt3)3 (M = FeII for I, CoII for II) clusters have been synthesized from the reaction between M(PEt3)2Cl2 and Na2tdt (tdt = toluene-3,4-dithiolate) in MeCN. Both complexes have been characterized by elemental analyses, FT-IR, UV–Vis, FAB-MS, 1H NMR and cyclic voltammetry. Structures of Fe3tdt3(PEt3)3 (I) and Co3tdt3(PEt3)3 (II) were determined by single crystal X-ray crystallography. The Fe3 triangular core of the 48-electron complex I, with an isosceles triangular geometry, showed very short Fe–Fe distances of 2.4014(13) and 2.4750(12) Å, which are comparable to the extensive M–M frameworks found in the FeMo-cofactor in nitrogenase. The isostructural Co3tdt3(PEt3)3 (II), with an analogous Co3 coordination geometry, showed short Co–Co distances of 2.4442(9) and 2.5551(10) Å. The slightly longer M–M distances in complex II were explained by a total valence electron counting argument. Cyclic voltammetry of Fe3tdt3(PEt3)3 (I) showed robust reduction waves compared to Co3tdt3(PEt3)3 (II). Temperature-dependent effective magnetic moment measurements of I and II showed both clusters behave similarly and the magnetic property of the M3 equilateral triangle core with extensive metal–metal interactions was characterized as degenerate frustration.Polyhedron 08/2007; 26(13):2949–2956. DOI:10.1016/j.poly.2007.01.052 · 2.05 Impact Factor