DELETION OF ANTENNA CHLOROPHYLL-A-BINDING PROTEINS CP43 AND CP47 BY TRIS-TREATMENT OF PS-II MEMBRANES IN WEAK LIGHT - EVIDENCE FOR A PHOTO-DEGRADATIVE EFFECT ON THE PS-II COMPONENTS OTHER THAN THE REACTION CENTER-BINDING PROTEINS

Treatment of spinach Photosystem II membranes by Tris (0.8 M, pH 7.5-10) in weak light (20-mu-E m-2 s-1) induced partial deletion of intrinsic proteins of PS II as well as release of three extrinsic proteins and Mn from the membranes. Most prominently deleted was CP43, which was detected by sodium dodecyl sulfate/ urea-polyacrylamide gel electrophoresis. D1 and CP47 were also affected by the same treatment but to a lesser extent. Deletion of CP43 did not occur when the PS II membranes were treated with Tris in the dark, or treated in the light in the presence of reductants for PS II. The results suggest that CP43 is located close to the water-oxidation site and is damaged by the oxidizing radicals produced at the oxidizing side of PS II during the Tris-treatment of the PS II membranes in the weak light. Difficulty in detecting the degradation products of CP43 indicates the high efficiency of the breakdown process of the protein.