SIMILARITY OF PRIMARY RADICAL PAIR RECOMBINATION IN PHOTOSYSTEM-II AND BACTERIAL REACTION CENTERS

We report temperature and magnetic field dependent measurements of the recombination dynamics of the radical pair P680+Pheo- in D1D2cytb559 reaction centers of photosystem II and compare the results to those ob tained in bacterial reaction centers. In photosystem II the rate of re combination to the groundstate is found to be slower than in the bacte rial reaction centers by a factor of at least 50. This difference aris es from the different redox potentials of the pigments of plant and ba cterial reaction centers. In contrast, the rate of recombination to th e triplet state is similar in all reaction centers, indicating a simil ar electronic coupling which allows us to conclude upon the structural similarity.