Nitrogenase ENDOR studies

Other Nitrogenase ENDOR Studies and Summary Comments... 

ENDOR Studies on the Resting State of Nitrogenase FeMo-cofactor... 

ENDOR Studies on Inhibitor States of the Nitrogenase FeMo-cofactor—Carbon Monoxide... 

ENDOR Studies on Substrate Analogue Turnover States of the Nitrogenase FeMo-cofactor—Ethyne... 

There are additional ENDOR studies on nitrogenase FeMo-cofactor that have not even been mentioned here. These include studies on the alternative substrate carbon disulfide. 

From a biochemical point of view, the summation of the ENDOR studies on nitrogenase FeMo-cofactor interacting with carbon-containing small molecules is an electron inventory of the resting state, lo-CO form, and ethyne-bound form (Sepri), resulting in the proposal that the resting state is two electrons more oxidized than the substrate/inhibitor-bound forms and further, that these forms could be placed into the context of the Lowe-Thomeley scheme of nitrogen fixation. 

From the point of view of inorganic chemistry, these ENDOR studies on nitrogenase FeMo-cofactor give definitive evidence of a remarkable series of bioorganometallic complexes, which should provide both a challenge and inspiration to synthetic chemists. 

Lukoyanov D, Pelmenschikov V, Maeser N, et al. Testing if the interstitial atom, X, of the nitrogenase molybdenum-iron cofactor is N or C ENDOR, ESEEM, and DFT studies of the S = 3/2 resting state in multiple environments. Inorg Chem. 2007 46 11437-49. 

J. Telser ed., Paramagnetic Resonance of Metallobiomolecules , ACS Symposium Series 858, American Chemical Society, Washington, DC, 2003, The author cannot be objective here, but this recent volume contains useful articles on ESEEM and ENDOR including case studies on nitrogenase, heme enzymes, FeS enzymes, and other areas. 

There are cases in which the total spin of the system under study is S > and the analysis of the hyperfine coupling in such systems must take into account the spin state of the system. Notable examples of this include ENDOR measurements on the Fe-Mo cluster of nitrogenase, whose EPR signal arises from the ms = doublet of an S = t system and ENDOR experiments on Mn centers, whose EPR signal can include contributions from all transitions within the manifold of spin states in the 5 = 1 system. 

For samples that are polycrystalline, including frozen solutions, ENDOR can give information about spatial relationships between electron spins and nuclei to which they are coupled. This is only possible in solid phases in which the EPR spectrum arises from all orientations of the paramagnetic species, and is therefore dominated by large anisotropic interactions. An example of an application of ENDOR to the study of nitrogenase is given in Section 12.19.2. 

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