The Correlation of Lipid Release and Photochemical Activities in Isolated Spinach Chloroplasts

Abstract

Purified isolated spinach chloroplasts were suspended in media of different pH and the extracts obtained after centrifugation were analyzed for their lipid composition. The quantity of lipids present in the supernatant increased considerably by lowering the proton concentration. Under alkaline conditions more than 30% of the phospho- and sulfolipids were released from the thylakoid membranes. A stabilization was achieved when higher concentrations of MgCl2 were present. Photochemical activities showed an uncoupling of photophosphorylation at pH 8.5 and 8.9, and a stabilization at pH 5.5. The correlation between phosphorylation and the release of lipids was further demonstrated in the presence of MgCl2 when the ATP-formation was protected under alkaline conditions. From the comparison of the lipid composition in the extracts obtained from broken chloroplasts and from fragments after sonication, the conclusion can be drawn that part of the phospho- and sulfolipids and monogalactolipids are located at the surface of the membrane. The majority of lipids released are bound to particles as demonstrated by the sedimentation in the ultracentrifuge.