Electron Paramagnetic Resonance Spectroscopy of the Iron-Molybdenum Cofactor of Clostridium pasteurianum Nitrogenase.
We report a computer simulation study of the electron paramagnetic resonance (EPR) spectral line shape of the iron-molybdenum cofactor of nitrogenase. The unusually broad and asymmetric line shape of the EPR spectrum can be interpreted in terms of a distribution of zero-field splitting parameters called D-strain. The best fit simulations were computed using D = 2.5 cm(-1) and E = 0.317 cm(-1) and distributions in D and E approximated by Gaussians of half-widths 0.446 cm(-1) and 0.108 cm(-1), respectively. The value of D estimated in the present work is smaller than previous estimates by others but consistent with the temperature dependence of the EPR spectrum. The large D-strain is most likely caused by an ensemble of nearly isoenergetic conformational states and should not be considered as being indicative of chemical inhomogeneity.
George
Graham N.
GN
Stanford Synchrotron Radiation Laboratory, Stanford University, SLAC MS 69, P.O. Box 4349, Stanford, California 94309, and Exxon Research and Engineering Company, Route 22 East, Annandale, New Jersey 08801.
Prince
Roger C.
RC
Bare
Richard E.
RE