Isolation of a photosystem 2 preparation from higher plants with highly enriched oxygen evolution activity

Detergent‐treatment of higher plant thylakoids with Triton X‐100 at pH 6.3 has been used to purify a PS2 fraction with very high rates of oxygen evolution (1000 μmol.mg chl −1 .h −1 ). A photosynthetic unit size of about 300 chlorophyll (chl) molecules has been determined by optical methods, suggesting an average turnover time for PS2 of about 2 ms. The donor system for P680 + is particularly well preserved in the preparation, as judged by P680 + reduction kinetics, the detection by EPR of Signal II LT and the presence of the high potential form of cytochrome b ‐559 (at a ratio of 1:1 with the reaction centre).