Inhibition of Photosystem 2 by Thylakoid Membrane Phosphorylation

Abstract

It is well established that several thylakoid membrane proteins can be reversibly phosphorylated (1). The two most heavily-labelled phosphoproteins, with molecular masses of 26 kDa and 24 kDa, have been identified as constituents of the light-harvesting chlorophyll a/b complex CLHCII). LHCII phosphorylation is thought to provide the molecular mechanism by which the chloroplast can alter the distribution of excitation energy between photosystem 2 (PS2) and PS1 (2,3). The identity and function of the other major thylakoid membrane phosphoprotein, with a molecular mass of 9 kDa, has not been determined. This phosphoprotein is associated with the PS2 reaction centre core (4), but is probably not the high redox potential cytochrome b₅₅₉ (5).