Absorption of visible light by ligand bound ferrous hemeproteins such as hemoglobin (Hb) and myoglobin (Mb) results in a near instantaneous (less than 10-13sec) rupture of the iron ligand bond. The photogenerated contact pair (heme plus ligand) can decay either through reformation of the iron-ligand bond (geminate recombination) or through a progressive increase in the iron ligand separation distance. The objective of this project is to determine the role conformational disorder plays in controlling or modulating geminate recombination in Hb and Mb at ambient temperatures. The following experiments are to be pursued: 1. A double pulse excitation experiment with sub picosecond resolution designed to determine the time scale over which the protein solution is effectively an inhomogeneous distribution of conformational substates. 2. A time resolved (less than 1picosecond resolution) kinetic hole burning experiment using Raman and absorption to characterize the spectra of fast and slow recombining conformations. 3. An experiment narrow sub designed to follow in real time the thermally driven dynamics of a population of conformational substates. The narrow distribution is to be generated by using a weak 620nm femtosecond excitation pulse. %%% A protein molecule can have any of a very large number of slightly different micro conformations. At biological temperatures, a given molecule undergoes rapid interconversion among these different conformational substates. It is possible that reactivity of a given protein is controlled by how frequently the protein assumes some highly reactive conformational substate.
