Protein dynamics studied on myoglobin

Two methods of inelastic scattering of synchrotron radiation were used to measure the dynamics of myoglobin in the temperature range from T = 60 K to 300 K. The inelastic Rayleigh scattering of metmyoglobin was analyzed by delayed elastic nuclear forward scattering of an iron foil. This yields averaged information on all phonons within the sample. The mean square displacement of the atoms due to this dynamics is 〈x²〉/T = 2.1 · 10^-4 ŲK^-1 on average. Complementary information was obtained by phonon assisted nuclear scattering on deoxymyoglobin. This method selects the phonons coupling to the iron atom in the active center of the protein. The mean square displacement of the iron was measured to be 〈x²〉/T = 0.6 · 10^-4 ŲK^-1. The results are in agreement with Mössbauer absorption experiments in the low temperature range. Above 200 K the results allow one to distinguish between harmonic and quasidiffusive dynamics within the protein. A comparison with Raman spectroscopy is made.