This research will use mutagenesis and ultrafast spectroscopy to investigate the early time mechanism of bacterial photosynthetic reaction centers by exploring the following issues: the control of electron transfer along the two symmetrically related electron transfer pathways, the role of the accessory bacteriochlorophylls in mediating energy transfer from the antenna, and the role of protein dynamics in the electron transfer reactions. In addition, single molecule fluorescence spectroscopy will be used to explore the energetics and decay times of early charge transfer intermediates in single reaction center/antenna complexes as well as the molecule-to-molecule variation in the transition energies of high-fluorescence reaction center mutants. Finally, photoactive yellow protein, a blue light sensory complex will be studied with ultrafast spectroscopy in order to understand the role of protein motion in the early time mechanism.
The mechanistic study of protein-mediated chemistry remains a central theme of modern biochemical research. Light driven biological reactions have been particularly amenable to dynamic studies in this area because reactions throughout the sample can be initiated and monitored with extraordinary kinetic resolution using modern pulsed-laser techniques. In this project mutagenesis and femtosecond spectroscopy will be used to study the role of the protein in controlling the pathway of electron transfer, the mechanism by which cofactors in the reaction center mediate capture of energy from the antenna, and the role of protein dynamics in the solar energy conversion reactions. In addition, the light emission from single photosynthetic complexes will be monitored in order to study how the thermodynamics of photosynthetic reactions changed from complex to complex. Finally, a study of the femtosecond dynamics of photoactive yellow protein, a blue light sensory complex involved in light-directed bacterial movement, will be initiated. In this system, protein motion is thought to be central to the mechanism.
