EFFECTS OF SYNTHETIC PEPTIDES ON THYLAKOID PHOSPHOPROTEIN PHOSPHATASEREACTIONS

A synthetic peptide analogue of the phosphorylation site of LHC II, wh en phosphorylated by thylakoid membranes, served as a substrate for th e thylakoid phosphoprotein phosphatase. The phosphopeptide became deph osphorylated at a low rate, comparable to that of the 9 kDa phosphopro tein. Phospho-LHC II itself became dephosphorylated much more rapidly, at a rate unaffected by endogenous phosphorylation of the peptide. En dogenous phosphorylation of the peptide was also without effect on oth er thylakoid protein phosphorylation and dephosphorylation reactions. In contrast, dephosphorylation of many thylakoid phosphoproteins was i nhibited by addition of a pure, chemically-synthesised phosphopeptide analogue of phospho-LHC II. This result suggests that at least one thy lakoid phosphoprotein phosphatase exhibits a broad substrate specifici ty. The results indicate that any one of a number of amino acid sequen ces can give a phosphoprotein configuration that is recognised by a si ngle phosphatase.