Phonon-assisted Mossbauer effect: The vibrational density of states of myoglobin

Proteins are involved in nearly all aspects of function and control of life. For many proteins, the structure alone cannot explain the function. Proteins often have to fluctuate to work. The fact that many proteins contain iron even within the active site, predestinate the various techniques of the Mossbauer effect to study these dynamics. The phonon-assisted Mossbauer effect allows the direct investigation of phonons in matter. This technique uses pulsed synchrotron radiation monochromized to about 1 meV energy bandwidth. For the present work, this method was used to yield information about the dynamics of myoglobin, the oxygen storing protein in vertebrates. It is shown that different ligands like CO or H2O at the iron site alter the local optical vibrations compared to ligand free deoxymyoglobin. Delocalised acoustic phonons can be resolved in the vicinity of the elastic line. The mode dependent mean square displacement of the iron, specific heat of vibration and second-order Doppler shift are obtained from the density of states.