Chloroplast Phosphoproteins

Abstract

When isolated, intact chloroplasts of pea ( Pisum sativum ) are incubated in the light with [ 32 P]‐orthophosphate, isotope is incorporated into several polypeptides. Among the most conspicuous phosphoproteins are two which form a very closely spaced doublet on dodecyl sulphate/polyacrylamide gels and co‐electrophorese with the major polypeptide component of the light‐harvesting chlorophyll a/b binding complex. Like the light‐harvesting polypeptide, the phosphoprotein doublet is bound to thylakoids, sediments with the heavy particles released from thylakoids after digitonin treatment, is soluble in chloroform/methanol and has an apparent molecular weight of about 26000. The doublet also appears in the highly purified light‐harvesting chlorophyll a/b binding complex isolated from thylakoids by hydroxylapatite chromatography. I conclude that two polypeptide components of the complex are phosphorylated. One of these components may be the major light‐harvesting chlorophyll a/b binding protein.