The reactivation properties for different anions in chloride depleted photosystem II membranes

Abstract

In photosystem II (PS II) membranes, chloride is needed for optimum oxygen evolution. Upon chloride depletion of PS II membranes the rate of oxygen evolution is suppressed to different levels depending on the choice of cryoprotectants. The rate in sucrose shows a higher degree of suppression than in glycerol. We have previously presented the one-site, two-state model for the binding of anions to chloride-depleted PS II membranes, in which switching occurs from an open state with loose binding to a closed, tight-binding state [Lindberg, K. and Andréasson, L.-E. (1996) Biochemistry 35, 14259-14267.]. This model is also valid when glycerol is used as a cryoprotectant with dissociation constants for chloride of 0.77 mM and 13 µM for the two states, respectively. We have characterized the behaviour of several anions (Cl-, Br-, I-, F- and NO3-) towards chloride-depleted PS II membranes in a glycerol medium. We will here report variations in the reactivation, binding affinity and kinetics of interaction of the different anions.