Use of Zinc Ions To Study Thylakoid Protein Phosphorylation and the State 1-State 2 Transition In Vitro

Abstract

At ATP concentrations < 0.2 mM, Zn ions cause a marked stimulation of endogenous protein phosphorylation in thylakoid membranes isolated from tobacco (Nicotiana tabacum L. cv. Turkish Samsum), pea (Pisum sativum L. cv. Feltham First ) and spinach (Spinacia oleracea L. cv. Northland). The greatest stimulatory effect was observed at Zn2+ concentrations of 1-2 mM; higher concentrations were inhibitory. The stimulatory effect of Zn2+ was independent of Mg2+ concentration from 1 to 5 mM and thus does not appear to be due to the formation of histones IIA, an exogenous protein substrate, was inhibited by 2 mM Zn2+. At low levels of ATP, Zn2+ not only stimulates general endogenous protein phosphorylation, but also the phosphorylation of the apoproteins of the light-harvesting chlorophyll a/b-protien complex. Under these conditions Zn2+ inhibits the ATP-induced quenching of photosystem II fluoresence and the increase in the ratio of photosystem I to photosystem II fluorescence which are both characteristic os the State 1-State 2 transition. These results suggest that phosphorylation of the light-harvesting chlorophyll a/b-protein complex may not directly bring about the State 1-State 2 transition.