EFFECT OF THE CA2-28392 ON REACTIVATION OF OXYGEN EVOLUTION OF CA2+-DEPLETED PHOTOSYSTEM-II( CHANNEL ACTIVATOR CGP)

The effect of the Calcium channel activator, CGP 28392, on the reactiv ation of oxygen evolution in Ca2+-depleted Photosystem LI (PS II) part icles has been investigated. Ca2+-binding is associated with a functio nal water splitting complex of PS II. In the presence of the activator , a low affinity site of Ca2+-binding is converted into a high affinit y 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 Ca2+-dependent reactivation of oxygen evol ution. The activator partially protects against this type of inhibitio n. It is suggested that the extrinsic proteins form a Ca2+ channel-lik e structure at the donor side of PS II.