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Protein dynamics at physiological temperatures

Picosecond vibrational spectroscopy is used to address a model problem in protein dynamics, that of how carbon monoxide and dioxygen reach the functional group in myoglobin. The spectra indicate that there is a metastable binding position for CO at 300 K with 60 ns lifetime. We use polarization dependent measurements and molecular dynamics software to assign the ligand's metastable location to a particular pocket in the protein. This location does not coincide with that which is determined by freezing out intermediates at low temperatures. The implications for the entry and exit trajectories of ligands in myoglobin are considered.