Arlt, Thomas; Schmidt, Stefan; Kaiser, Wolfgang; Lauterwasser, Christoph; Meyer, M.; Scheer, Hugo; Zinth, Wolfgang (1993): The accessory bacteriochlorophyll. a real electron carrier in primary photosynthesis. In: Proceedings of the National Academy of Science of the United States of America, Vol. 90, Nr. 24: S. 11757-11761




The primary electron transfer in reaction centers of Rhodobacter sphaeroides is studied by subpicosecond absorption spectroscopy with polarized light in the spectral range of 920-1040 nm. Here the bacteriochlorophyll anion radical has an absorption band while the other pigments of the reaction center have vanishing ground-state absorption. The transient absorption data exhibit a pronounced 0.9-ps kinetic component which shows a strong dichroism. Evaluation of the data yields an angle between the transition moments of the special pair and the species related with the 0.9-ps kinetic component of 26 +/- 8 degrees. This angle compares favorably with the value of 29 degrees expected for the reduced accessory bacteriochlorophyll. Extensive transient absorbance data are fully consistent with a stepwise electron transfer via the accessory bacteriochlorophyll.