Role of heme propionates of myoglobin in vibrational energy relaxation

The role of heme propionates of myoglobin in vibrational energy relaxation was studied by time-resolved resonance Raman spectroscopy. Time-resolved anti-Stokes spectra were measured to monitor the vibrational energy relaxation of the heme. The decay rates of the band intensities were compared between wild-type myoglobin and etioheme-substituted myoglobin where the heme lacks hydrogen-bonding side chains. The decay rates of the anti-Stokes intensities of the latter were less than those of the former, providing strong support for a theoretical proposal that the propionates and their coupling to solvent bath play an important role in the dissipation of excess energy of the excited heme in solvated wild-type myoglobin.