Physics of proteins at low temperature

We present results of a hole burning study with thermal cycling and waiting time spectral diffusion experiments on a modified cytochrome - c protein in its native as well as in its denatured state. The experiments show features which seem to be characteristic for the protein state of matter and its associated dynamics at low temperature. The properties responsible for the observed patterns are organisation paired with randomness and, in addition, the finite size which gives rise to surface and solvent effects. We discuss some general model approaches which might serve as guide lines for understanding these features.