Dielectric relaxation models applied to the dynamics of myoglobin as determined by Mössbauer spectroscopy

Protein specific modes of motions are found in myoglobin crystals above 180 K. In this contribution we show that this type of motions can be analyzed by a Davidson-Cole, a Cole-Cole or a Havriliak-Negami distribution in analogy to dielectric relaxation. However, the temperature dependence of the obtained parameters is quite unusual indicating a broadening of the distributions with temperature instead of motional narrowing. This can be understood from the picture of conformational substates if one assumes that more and more substates become accessible with increasing temperature. The result shows that the analogy between glass forming organic liquids and proteins should not be exaggerated.