Electron transfer mechanism in the reaction center of photosynthetic bacteria

The structure of the photosynthetic reaction center recently resolved by Deisenhofer et al. is discussed in relation to design principles for energy-storing systems. The rates of the primary electron transfer reactions are deduced by taking the electronic structure of the chromophores and their geometrical arrangement explicitly into account, while the protein portion is considered as a dielectric continuum which is rigid to an extent that the free-energy loss by solvent reorganization can be neglected. The values of the different rate constants thus obtained are in good agreement with experimental data. Each chromophore component in the reaction center appears to be positioned optimally for the purpose of energy storage in electron transfer. This can be shown by repeating the calculations for various arrangements that differ somewhat from the arrangement obtained by Deisenhofer et al. The device can only operate as an energy-storing system if each functional component molecule is exactly adjusted to each other sterically and energetically. It is shown by proposing a reasonable evolutionary pathway that the emergence of the specific arrangement of chromophores and proteins in the reaction center can be made plausible.