Protein structural dynamics as determined by Mössbauer spectroscopy

Mössbauer spectroscopy on⁵⁷Fe allows the study of dynamics with a characteristic time faster 100 ns. For myoglobin a detailed physical picture of protein dynamics has been obtained. A myoglobin molecule has no well defined energy minimum. X-ray structure analysis yields only an average conformation. At low temperatures the molecules are trapped in slightly different structures called conformational substates. At higher temperatures a Brownian type of oscillation of molecular segments in restricted space occurs. RSMR technique allows an estimation of the characteristic size of these segments which are in myoglobin well below 30 A and larger than 6 A. A determination of the quasielastic absorption with high accuracy yields the energy distribution of the conformational substates. As further examples bacteriorhodopsin and a model compound for membranes are discussed.