Significant species-dependence of P700 redox potential as verified by spectroelectrochemistry: Comparison of spinach and Theromosynechococcus elongatus

The redox potentials of P700, the primary electron donor of photosystem (PS) I, of spinach and Thermosynechococcus elongatus were determined by means of spectroelectrochemistry with an error range of ±2–3mV, to find that the redox potential of P700 in T. elongatus is lower by ca. 50mV as compared with spinach. The shift in the P700 redox potential of PS I core particles prepared by harsh detergent treatments remained to within 10mV for both organisms. These results show that the 50mV difference in the P700 redox potential between the two organisms is not a detergent-induced artifact but reflects an intrinsic property of each PS I.