Nuclear forward scattering of synchrotron radiation by deoxymyoglobin

Nuclear forward scattering of synchrotron radiation is used to determine th e quadrupole splitting and the mean square displacement of the iron atom in deoxymyoglobin in the temperature range between 50 K and 243 K. Above 200 K an abnormally fast decay of the forward scattered intensity at short time s after the synchrotron flash is observed, which is caused by protein-speci fic motions. The results strongly support the picture that protein dynamics seen at the position of the iron can be understood by harmonic motions in the low temperature regime while in the physiological regime diffusive moti ons in limited space are present. The shape of the resonance broadening fun ction is investigated. An inhomogeneous broadening with a Lorentzian distri bution indicating dipole interactions results in a better agreement with th e experimental data than the common Gaussian distribution.