The existence of a high photochemical turnover rate at the reaction centers of system II in Tris-washed chloroplasts.

In Tris-washed chloroplasts the kinetics of the primary electron acceptor X 320 of reaction center II has been investigated by fast repetitive flash spectroscopy with a time resolution of approximately 1 mus. It has been found that X 320 is reduced by a flash in less than or equal to 1 mus. The subsequent reoxidation in the dark occurs mainly by a reaction with a 100-200 mus kinetics. The light-induced difference spectrum confirms X 320 to be the reactive species. From these results it is concluded that in Tris-washed chloroplasts the reaction centers of System II are characterized by a high photochemical turnover rate mediated either via rapid direct charge recombination or via fast cyclic electron flow.