Thylakoid membrane protein phosphorylation in correlation with photosynthetic membrane activation

The phosphorylation of five $\text{E.}\text{gracilis}$ thylakoid membrane polypeptides was studied, in isolated chloroplasts. Using [³²P] labelling, in the light, we found that phosphorylation was inhibited by ethanol and DCMU. Inhibition curves were characteristic of photosynthetic inhibition. [γ-³²P] ATP labelling was used to distinguish between two groups of phosphoproteins: the first one, includes protein I, II, V which require only ATP for phosphorylation while the second one includes protein III and IV whose phosphorylation is light-requiring. Phosphorylation of protein III and IV was inhibited by CCCP, NH₄Cl and DCMU, and was reversible in the dark.