Internal vibrational energy redistribution precedes energy dissipation into the solvent upon photoexcitation of heme proteins

Efficient energy dissipation is a fundamental property of proteins that has been challenging to observe. This study investigates the mechanism of energy flow from excited heme proteins into the surrounding solvent using optical-pump THz-probe spectroscopy. The results were compared with a computational model of the energy flow. We find that the experimentally observed time constants of 6.1 ± 0.3 ps and 7.3 ± 0.4 ps for cytochrome <i>c</i> and myoglobin are in excellent agreement with the computational model. This suggests a diffusive energy transfer for the release of excitation energy from the excited heme group through the protein as the dominant pathway of energy flow to the surrounding solvent in heme proteins. We also observe a notable isotope effect suggesting a complex coupling of the protein to the solvent.