Correlating Ultrafast Function with Structure in Single Crystals of the Photosynthetic Reaction Center

Femtosecond transient absorbance spectroscopy was applied to the study of primary electron transfer in single reaction center crystals from Rhodobacter sphaeroides. Polarized transient absorption spectra of individual crystals are shown to correlate with polarized ground-state absorption spectra and to track cofactor transition moment directions calculated from the crystallographic structure. Electron transfer from the bacteriochlorophyll dimer to the bacteriopheophytin acceptor was found to be multiphasic in crystals and ∼2-fold slower than in solution. This work demonstrates the ability to resolve ultrafast photosynthetic function in single crystals and allows ultrafast function to be directly correlated with structure.