RATE-PROCESSES IN PROTEINS

Flash photolysis experiments on carbonmonoxymyoglobin over wide ranges in time and temperature provide information about the rate processes involved in the rebinding reaction. The non-exponential rebinding at low temperatures shows that the myoglobin molecules are frozen into a large number of conformational substates with different enthalpic barriers. Above 160 K we observe a relaxation process that shifts the peak of the barrier distribution from approximately 10 kJ/mol to approximately 21 kJ/mol. This process is nonexponential in time and does not obey the Arrhenius law. Above 220 K equilibrium fluctuations between the conformational substates lead to an averaging of the binding rate distribution and to the opening of pathways for the ligands to escape from the protein molecules.