The influence of electrostatic interactions and intramolecular dynamics on electron transfer from the cytochrome subunit to the cation - Radical of the bacteriochlorophyll dimer in reaction centers from Rps viridis

Interheme electrostatic interaction can explain the acceleration of the electron transfer (ET) rate from the highest potential heme (C-380) to the photooxidized bacteriochlorophyll dimer (P+) which takes place after the reduction of neighbouring heme(s) of the cytochrome subunit in the reaction center of Rps. viridis. The electrostatic interaction energies calculated fur neighbouring hemes, 7.0 Angstrom apart (edge to-edge), and for two high potential hemes, 21.5 Angstrom apart are found to be 0.110 eV and 0.030 eV respectively. The reorganisation energy of the C-380-P+ transition of about 0.290+/-0.030 eV is calculated using the Marcus theory of electron tunneling. An empirical relation for the rate of ET is given. The low temperature restriction of the C-380-P+ transition is caused by an energetic inhibition which originates from an opposite shifting of the energy levels of C-380 and P+ due to the freezing of protein dynamics and protein-bound water mobility. The freezing of the protein dynamics is revealed by the Mossbauer effect and correlates with the efficiency of the ET.