Protein dynamics at low temperatures

The low temperature conformational dynamics of the heme type protein mesopo rphyrin-IX-substituted horseradish peroxidase is investigated by spectral d iffusion waiting time/aging experiments. Spectral diffusion broadening is g overned by a power law in time. There is a small but significant aging effe ct. It is assumed that the conformational dynamics of the protein which lea ds to the spectral broadening of the burnt-in holes is governed by a diffus ion type equation. In this case the shape of the spectral diffusion kernel is Gaussian. This model is contrasted with spectral diffusion phenomena as described by the TLS-model (TLS, two level system). (C) 2000 American Insti tute of Physics. [S0021-9606(00)50306-7].