Beschreibung:
Phosphorylation of polypeptides in whole cells and in chloroplasts of different strains of Chlamydomonas reinhardii was studied. Phosphorylation in vivo was strongly reduced when cytoptasmic protein synthesis was inhibited either by anisomycin or by cycloheximide. In isolated chloroplasts these two inhibitors had no effect on labelling. The incorporation of [32P]‐phosphate into one of the apoproteins of the light‐harvesting chlorophyll a/b‐protein complex (LHC 2) was also studied in relation to its synthesis. In vivo, in a chlorophyll b‐deficient mutant and in its parent strain we found a pronounced relationship between synthesis and phosphorylation of this LHC 2‐apoprotein. Our results suggest that LHC 2‐apoproteins, newly synthesized in the cytoplasm, are preferentially phosphorylated after synthesis. Together with the observation that phosphorylation still occurs in isolated chloroplasts we conclude that in vivo at least two levels of phosphorylation of the LHC 2‐apoproteins have to be clearly differentiated. One level involves the phosphorylation of existing and the other of newly synthesized polypeptides. The biological significance of phosphorylation of the LHC 2‐apoproteins in vivo and probably also of other thylakoid polypeptides is complex and not restricted to regulation of energy distribution between photosystems 1 and 2.