Photosynthetic oxygen evolution does not require the participation of polypeptides of 16 and 24 kilodaltons.

Oxygen evolution from Triton X-100 prepared photosystem II particles from spinach was inhibited 70-80% after treatment of the particles with high concentrations of salt (0.5 or 1 M NaCl). The salt-washed preparations were depleted of 16 and 24 kilodalton polypeptides. Nearly complete restoration of herbicide-sensitive electron transport activity was observed upon addition of Cl-. Maintenance of the maximal rates required the presence of Ca2+. Restoration of the activity did not require the readdition (reconstitution) of the extracted polypeptides indicating that the 16 and 24 kilodalton polypeptides do not participate directly in the water-oxidation process. They may, however, play a regulatory role, e.g., in the sequestering of Cl- and/or Ca2+.