Rayleigh and Brillouin scattering in a lysozyme-water mixture: An unusual behavior around 343Â K

This article describes Rayleigh and Brillouin light scattering studies on a lysozyme-water mixture from 293 K to 355 K. The scattering intensities from this system are compared with those from a sodium acetate buffer used to dissolve the lysozyme. It is found that in the vicinity of 343 K the lysozyme-water mixture becomes opalescent, and the intensity of the Brillouin peaks decreases and almost vanishes, to be restored at temperatures above 343 K. Around the same temperature the intensity of the central, unshifted Rayleigh peak, however, increases strongly. No such behavior was observed for the sodium acetate buffer. The analysis of the experimental data indicates an irreversible transition, near 343 K, from a metastable buffered system containing folded lysozyme molecules to a multimolecular gel of thermally unfolded lysozyme molecules.