Regulation of Photosystem II core protein phosphorylation at the substratelevel: Light induces exposure of the CP43 chlorophyll a protein complex tothylakoid protein kinase(s)

Light induces conformational changes in the CP43 chl-a-protein antenna comp lex in isolated PS II core-complexes exposing phosphorylation site(s) to PS II core-associated protein kinase(s), to added solubilized thylakoid prote in kinase(s), as well as to tryptic cleavage. The substrate-activation effe ct is demonstrated by exposure of the PS II cores to light during the kinas e assay as well as by preillumination of the PS II cores in which the endog enous kinase(s) has been inactivated by treatment with N-ethylmaleimid. In the latter case, phosphorylation was performed in darkness following additi on of the solubilized protein kinase(s). The solubilized protein kinase(s) does not require light activation. The apparent molecular masses of the mai n protein kinase(s) associated with the PS II cores (about 31-35 kDa and 45 kDa) differ from that of the major protein kinase present in solubilized p reparations obtained from spinach thylakoids (64 kDa). The light-induced ex posure of CP43 increases with the light intensity in the range of 20-100 mu mol photons m(-2) s(-1) as demonstrated by preillumination of N-ethylmalei mid treated cores followed by addition of the solubilized protein kinase(s) and performing the phosphorylation assay in darkness.