title: Electron Paramagnetic Resonance Spectroscopy of the Iron-Molybdenum Cofactor of Clostridium pasteurianum Nitrogenase.
abstract: 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.
authors.affiliation: 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.
authors.forename: Graham N.
authors.initials: GN
authors.lastname: George
authors.forename: Roger C.
authors.initials: RC
authors.lastname: Prince
authors.forename: Richard E.
authors.initials: RE
authors.lastname: Bare