Vibrational Echo Studies of Heme-Protein Dynamics

The first picosecond infrared vibrational echo experiments on a protein, myoglobin-CO, are described. The experiments, performed over a temperature range of 50-300K, with native and mutant myoglobin in different solvents, provide information about protein dynamics occurring on the 10^-12-10^-10 s time scales, which influence the vibrational transition of the CO ligand bound to the active site. The experiments reveal the existence of a protein energy landscape with a relatively flat distribution of energies between conformational minima, which interconvert via tunneling at lower temperature and by activated processes at ambient temperature.