Use of synthetic peptides to study the substrate specificity of a thylakoid protein kinase

Abstract

Seven synthetic peptide analogs of the phosphorylation site of the light‐harvesting chlorophyll a/b complex II (LHC II) were used to examine the substrate specificity of thylakoid‐bound LHC II kinase in higher plants. The peptides were phosphorylated by spinach and pea thylakoid membranes in which LHC II kinase had been activated by illumination. Phosphorylation was under redox control, as shown by the inhibitory ability of 20μM diuron. Apparent K _m(peptide) values ranged from 26 μM for a highly basic peptide with multiple sites for phosphorylation to 1.2 mM for a peptide lacking basic residues on the N‐terminal side of the phosphorylation site. Both serine and threonine residues were phosphorylated but the relative rates depended on peptide sequence. A comparison of our data with published LHC II sequences indicates that almost all known LHC II molecules have phosphorylatable sequences.