Primary photosynthesis in reaction centers containing four different types of electron acceptors at site HA Original Research Article

Femtosecond spectroscopy is used to study the primary electron transfer reactions in photosynthetic reaction centers, where the chromophore at the secondary acceptor site is changed from bacteriopheophytin a via 3-vinyl-bacteriopheophytin a and 3-acetyl-pheophytin a to pheophytin a. Pronounced changes in the primary electron transfer reactions are observed which are directly related to the redox potential of the different chromophores and the corresponding changes in free energy of the first intermediates. The reaction dynamics do not primarily correlate with the changes in absorption spectra.