Abstract
The redox potential of P700, the primary electron donor of Photosystem (PS) I, was determined spectroelectrochemically with optically transparent thin-layer cells under strict control of electrode potential. The P700 redox potential of PS I isolated from a thermophilic cyanobacterium Thermosynechococcus elongatus (+425 mV vs. SHE) was by about 50 mV lower than that in spinach (+475 mV). The P700 redox potential was affected by < 10 mV by treatments with various concentrations of Triton X-100, indicating that the observed difference in the P700 redox potential between the two organisms was not a detergent-induced artifact but intrinsic properties of both P700. The P700 potentials of a cyanobacterium Synechococcus PCC6301 and a green alga Chlorella vulgaris (+453 mV) showed an intermediate value between T. elongatus and spinach. These results suggest that P700 in various organisms could be classified into at least three types based on its redox potential.
