Ultrafast time-resolved IR studies of protein-ligand interactions.

Time-resolved mid-IR spectroscopy combines molecular sensitivity with ultrafast capability to incisively probe protein-ligand interactions in model heme proteins. Highly conserved residues near the heme binding site fashion a ligand-docking site that mediates the transport of ligands to and from the binding site. We employ polarization anisotropy measurements to probe the orientation and orientational distribution of CO when bound to and docked near the active binding site, as well as the dynamics of ligand trapping in the primary docking site. In addition, we use more conventional transient absorption methods to probe the dynamics of ligand escape from this site, as well as the ultrafast dynamics of NO geminate recombination with the active binding site. The systems investigated include myoglobin, hemoglobin, and microperoxidase.