Dear ifeffit mailing list recipients, See seminar details below, and please send recommendations for speakers. Jerry Seidler (seidler@uw.edu) ------------------------------------ *Deciphering the Dynamics of the Ferrous Cytochrome c Photodissociative State Using Ultrafast X-ray Spectroscopy and Scattering Methods* Prof. Michael Mara (Northwestern University) Thursday August 26: 9 am Seattle (PDT), 12 noon NY, 5 pm London, 6 pm Berlin, 7 pm Moscow link: https://washington.zoom.us/j/92742942089 password: EXAFS *Abstract*: The femtosecond X-ray pulses provided by X-ray free electron lasers enable tracking of electronic and structural dynamics in metalloprotein active sites immediately following photoexcitation. Here, we decipher the evolution of the photodissociated state of ferrous cytochrome c using Fe K-edge X-ray absorption and emission spectroscopies, as well as X-ray solution scattering. By absorption and emission methods, we track the rebinding of the cleaved ligand and identify an electronic intermediate state involved in ligand dissociation. X-ray scattering further defines the early-time active site structure while following heat dissipation from the hot ground state of the active site into the solvent. By relating the active site temperature to the kinetics of ligand recombination, we quantify the protein bulk contribution to stabilizing the protein iron-methionine bond; this is the first direct measurement of the protein entatic state, whereby the protein regulates activity through modest tuning of the energetics of the active site. *Suggested reading:* [1] Mara, M. W. et al., Metalloprotein entatic control of ligand-metal bonds quantified by ultrafast x-ray spectroscopy, Science, 2017, 356, 1276-1280. https://science.sciencemag.org/content/356/6344/1276.full [2] Reinhard, M. E. et al, Short-lived metal-centered excited state initiates iron-methionine photodissociation in ferrous cytochrome c, Nature Communications, 2021, 12, 1086. https://doi.org/10.1038/s41467-021-21423-w -- *Gerald Seidler* *Professor, Physics Department* *University of Washington* *http://faculty.washington.edu/seidler/index.html http://faculty.washington.edu/seidler/index.html* *seidler@uw.edu *