FURTHER CHARACTERIZATION OF THE LOSS OF ANTENNA CHLOROPHYLL-BINDING PROTEIN CP43 FROM PHOTOSYSTEM-II DURING DONOR-SIDE PHOTOINHIBITION

The photo-induced reduction in the level of the antenna chlorophyll-binding proteins CP43 and CP47, as well as the reaction-center-forming protein D1, in Photosystem II was studied with PS II membranes and PS II complexes that had been treated with alkaline Tris. The loss of CP43, as detected by sodium dodecyl sulfate/urea polyacrylamide gel electrophoresis, was attributed mostly to specific cross-linking reactions among CP43, CP47 and the D1 protein. The cross-linking of the D1 protein and the alpha-subunit of cytochrome b-559 was also observed. The cross-linking reaction was stimulated by elevated pH and temperature, but it was independent of oxygen. The addition of cations induced a simultaneous decrease in the amount of the product of cross-linking between CP43 and the D1 protein and increase in the amounts of a 38 kDa cross-linking form of the D1 protein and a 16 kDa degradation product of the D1 protein. These results indicate that the cross-linking of the proteins in the PS II complex and the degradation of the D1 protein during photoinhibition are closely related and electrostatically regulated. The cross-linking between CP43 and the D1 protein probably affects the efficiency of degradation of the D1 protein.