Relationships between protein phosphorylation and electron transport in the reconstituted chloroplast system

Phosphorylation of the light-harvesting chlorophyll protein (LHCP) by the thylakoid protein kinase has been examined in the reconstituted chloroplast system. The level of phosphorylation by [32P]Pi was maximal at high light intensity and in the absence of 3-phosphoglycerate; dephosphorylation resulted from a subsequent decrease in light intensity or from the addition of 3-phosphoglycerate. Addition of ribose 5-phosphate, which acts as an ATP 'sink', also caused dephosphorylation. It is concluded that the degree of phosphorylation is dependent on the redox state and energy state of the system, thereby providing a mechanism for adapting light harvesting to the demands of carbon assimilation.