A Light-dependent Protein Kinase Activity of Chloroplasts

A protein kinase activity from spinach chloroplasts, tightly associated with the thylakoid membranes, has been solubilized and partially characterized. This membrane-bound protein kinase is stimulated by light and electron transport activity through photosystem II appears to be required for stimulation.Electron transport inhibitors like 3,4-dichlorophenyl-1,1-dimethylurea, Tris, and NH(2)OH treatments, inhibit the light activation process. Furthermore, after Tris inhibition, the protein kinase activity is restored by washing the Tris-treated chloroplasts with dichlorophenol indophenol plus ascorbate. The protein kinase remains active in the dark after short illumination periods, suggesting that a product of electron transport may be involved in light activation.Two endogenous substrates of the protein kinase in thylakoid membranes are the N,N'-dicyclohexylcarbodiimide-reactive proteolipid and the light-harvesting chlorophyll-protein complex. The membrane-bound protein kinase also phosphorylates externally added histone.