Selective and specific cleavage of the D1 and D2 proteins of Photosystem II by exposure to singlet oxygen: Factors responsible for the susceptibility to cleavage of the proteins

Exposure of isolated Photosystem II (PS II) complexes to singlet oxygen (O-1(2)) results in cleavage of the D1 protein to specific fragments as does illumination with strong light (Mishra, N.P. and Ghanotakis, D.F, (1994) Biochim. Biophys. Acta 1187, 296-300). We reexamined the effects of O-1(2), generated by the photosensitizing reaction of rose bengal, on proteins of the PS II complexes. It was found that the D1 protein and also the D2 protein wen selectively cleaved into specific fragments as under strong illumination. This observation suggests that only the D1 and D2 proteins have amino acid sequences that are cleavable after attack by O-1(2). These two proteins were almost equally susceptible to cleavage by O-1(2). By contrast, when the PS II complexes that had been solubilized with SDS were exposed to O-1(2), no distinct fragments of the D2 protein were detected, while the D1 protein was cleaved to specific fragments, though the yield of fragments was about half of that obtained from the intact PS II complexes, These results imply that the conformation of proteins is crucial for the specific cleavage by O-1(2), and that only the D1 protein could retain the conformation required for the cleavage, though partly, after solubilization with SDS.