Current Research

Theoretical study on vibrational relaxation process of photoexcited MbCO

Photoexcitation of carboxymyoglobin (MbCO) triggers the ligand photolysis and, concomitantly, the heme comes to have excess vibrational energy. Then, the excess energy relaxes into the surrounding globin and, finally, into water solvent. Femtosecond IR spectroscopy experiments have revealed that the heating of the surrounding water is a biphasic process. The slow process can be explained by the isotropic classical thermal diffusion. But, it remains an unsettled question whether the fast process might be dominated by the energy transfer through the propionate side chains of the heme or through the collective motions of the globin matrix. In order to elucidate the detailed relaxation path, full-atomic molecular dynamics (MD) simulations of MbCO in explicit water solvent are executed for theoretical investigations. Since we focus especially on the statistical reliability, a large number (several hundreds) of MD simulations are executed for the ensemble-average, i.e., the ensemble MD method.