Absorption of light by photosynthetic reaction centers causes structural changes and triggers a series of electron transfer reactions, resulting in a transmembrane potential difference that can be used to drive the subsequent chemistry. The initial electron transfer generates a charge-separated state that must be stabilized to prevent dissipation of energy through recombination. Wöhri et al. have used time-resolved Laue diffraction crystallography to observe light-induced conformational changes that occur within milliseconds of photooxidation of the dimer of bacteriochlorophyll molecules, known as the “special pair,” in the photosynthetic reaction center of Blastochloris viridis. Stabilization appears to occur because of the deprotonation of a conserved tyrosine residue that moves closer to the special pair.
A. B. Wöhri, G. Katona, L. C. Johansson, E. Fritz, E. Malmerberg, M. Andersson, J. Vincent, M. Eklund, M. Cammarata, M. Wulff, J. Davidsson, G. Groenhof, R. Neutze, Light-induced structural changes in a photosynthetic reaction center caught by Laue diffraction. Science 328, 630–633 (2010). [Abstract] [Full Text]