Reorganization energies of the electron transfer reactions involving quinones in the reaction center of Rhodobacter sphaeroides

Abstract

In framework of the continuum electrostatics theory, the reorganization energies of the electron transfers Q_A^--Q_B (fast phase), Bph^--Q_A, P⁺-Q_A^-, and P⁺-Q_B^- in the photosynthetic bacterial reaction center have been calculated. The calculations were based on the static dielectric permittivity spatial distribution derived from the data on the electrogenesis, with the corresponding characteristic times relatively close to the reaction times of Q_A^--Q_B (fast phase) and Bph^--Q_A but much shorter than those times of the latter two recombination reactions. The calculated reorganization energies were reasonably close to the experimental estimates for Q_A^--Q_B (fast phase) and Bph^--Q_A but substantially lower than those of P⁺-Q_A^- and P⁺-Q_B^-. A higher effective dielectric permittivity contributes to this effect, but the dominant contribution is most probably made by a non-dielectric relaxation, especially for the P⁺-Q_B^- recombination influenced by the proton transfer. This situation calls for reconsidering of the current electron transfer rate estimates.

Keywords: Dielectric inhomogeneity of protein; Electron transfer; Photosynthesis; Quinone; Reorganization energy.