Anomalous temperature behavior of hypersonic acoustic phonons in a lysozyme crystal

The behavior of acoustic phonons in tetragonal lysozyme crystals is studied using Brillouin scattering over a temperature range from 298 to 330 K. Around 307 K, anomalies in the temperature dependence of the velocity and integral intensity of a quasi-transverse phonon and in the velocity of a quasi-longitudinal phonon are detected. The experimental results are discussed in terms of the current concepts of the dynamics of proteins. The observed anomalies in the behavior of hypersonic acoustic phonons are indicative of a structural phase transition occurring in a lysozyme crystal at 307 K.