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 obtained in bacterial reaction centers. In photosystem II the rate of recombination to the groundstate is found to be slower than in the bacterial reaction centers by a factor of at least 50. This difference arises from the different redox potentials of the pigments of plant and bacterial reaction centers. In contrast, the rate of recombination to the triplet state is similar in all reaction centers, indicating a similar electronic coupling which allows us to conclude upon the structural similarity.