Molecular composition of cyanobacterial phycobilisomes

Phycobilisomes isolated from eight different species of cyanobacteria contain in addition to the light-harvesting phycobiliproteins, a small number of colorless polypeptides with molecular weights higher than those of the chromopolypeptide subunits of the phycobiliproteins. In the phycobilisomes of the species examined, from four to nine colorless polypeptides were resolved by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Those of highest molecular weight (70,000-120,000) also occurred in the washed membrane fraction of the cell and may therefore be derived from the thylakoids, to which the phycobilisomes are attached in vivo. Colorless polypeptides of lesser molecular weight (30,000-70,000) appeared to be specific constituents of the phycobilisome. In strains of cyanobacteria that adapt chromatically, their synthesis, like that of the major phycobiliproteins, is regulated by light quality.