Effect of the Ca2+ channel activator CGP 28392 on reactivation of oxygen evolution of Ca(2+)-depleted photosystem II

The effect of the Calcium Channel Activator, CGP 28392, on the reactivation of oxygen evolution in CA(2+)-depleted Photosystem II (PS II) particles has been investigated. CA(2+)-binding is associated with a functional water splitting complex of PS II. In the presence of the activator, a low affinity site of CA(2+)-binding is converted into a high affinity binding site. Following removal of the extrinsic proteins (17 and 23 kDa), any effect of the activator is no longer observed. Ca2+ channel inhibitors can inhibit the CA(2+)-dependent reactivation of oxygen evolution. The activator partially protects against this type of inhibition. It is suggested that the extrinsic proteins form a Ca2+ channel-like structure at the donor side of PS II.