  We examine temperature dependent picosecond dynamics as a function of
structure and function for lysozyme and cytochrome c using temperature
dependent terahertz permittivity measurements. A double Arrhenius temperature
dependence with activation energies E1 ~ 0.1 kJ/mol and E2 ~10 kJ/mol fits the
native state response. The higher activation energy is consistent with the
so-called protein dynamical transition associated with beta relaxations at the
solvent-protein interface. The lower activation energy is consistent with
correlated structural motions. When the structure is removed by denaturing the
lower activation energy process is no longer present. Additionally the lower
activation energy process is diminished with ligand binding, but not for
changes in internal oxidation state. We suggest that the lower energy
activation process is associated with collective structural motions that are no
longer accessible with denaturing or binding.
