It's Swinging Time: Prolonged Energy Release of Myoglobin upon CO Dissociation

Nonequilibrium energy redistribution in proteins and their surrounding solvent upon photoexcitation and chemical reactions can have a significant impact on biological processes. Heme proteins are of central importance for oxygen transport and storage and electron transport. In the present study, we follow for the first time energy redistribution subsequent to photodissociation of carbon monoxide (CO) from myoglobin (Mb) by optical pump-terahertz probe spectroscopy (OPTP), directly monitoring the energy release into the low-frequency collective water modes. Our experiments reveal that energy release upon CO dissociation prolongs the solvent response by approximately 1 ps compared to photoexcitation of ligand-free Mb in both H2O and D2O. Based on the combined study with molecular modeling (MM), we propose that a "swinging motion" of the heme pocket extends the time for excess energy from the reaction to flow into the solvent. These findings reveal the coupling pathway of the intraprotein dynamics and solvent reorganization during the dissipation of nonequilibrium energy.