Rates of release and binding of Cl− from/to its action site in the O2 evolving reaction in photosystem II particles derived from spinach chloroplasts were estimated by measuring the suppression of O2 evolution by salt addition (ionic-jump) and its recovery by the readdition of Cl−. It was estimated that depletion and rebinding of Cl− were completed within a few seconds. These results suggest that the Cl−-action site is located in a space which is almost freely accessible to various ions in the outer medium, with no barrier to ion movements. These results can be explained by electrostatic attraction of Cl− to its action site, as was proposed in a study of anion effects on O2 evolution [(1986) Plant Cell Physiol. 27, in press].
