Theoretical study on primary reaction of photosynthetic bacteria

Theoretical calculation was carried out on the primary electron donor P870 of photosynthetic bacteria. The results show that: (i) the bimolecular structure of the primary electron donor is more advantageous in energy than monomolecular structure; (ii) the initial configuration of primary electron donor is no longer stable and changes to the configuration with lower energy and chemical reactivity after the charge separation. In the P870, such structural change is completed through the rotation of C3 acetyl, so the oxygen atom of acetyl interacts with the magnesium atom of another bacterio-chlorophyll molecule, and the total energy and chemical reactivity are reduced evidently. It is suggested that the structural change of the primary electron donor is important in preventing the occurrence of charge recombination during the primary reaction and maintaining the high efficiency of the conversion of sun-light to chemical energy. A new mechanism of primary reaction has been proposed, which can give reasonable explanations to the results of kinetic and site mutation studies.