A new model of phycobilisome in Spirulina platensis

Phycobilisomes (PBS) were isolated from blue-green alga Spirulina platensis . Scanning tunneling microscope was used to investigate the three-dimension al structure of PBS deposited on freshly cleaved highly oriented pyrolytic graphite (HOPG) in ambient condition at room temperature. The results showe d that the rods of PBS radiated from the core to different directions in th e space other than arrayed in one plane, which was different from the typic al hemi-discoidal model structure. The diameter of PBS was up to 70 nm, and the rod was approximately 50 nm in length. Similar results were observed i n Langmuir-Blodgett (LB) film of PBS. The dissociated PBS could reaggregate into rod-like structures and easily form two-dimensional membrane while be ing absorbed on HOPG, however, no intact PBS was observed. The filling-spac e model structure of PBS in Spirulina platensis with STM from three-dimensi onal real space at nanometer scale was found, which showed that this new st ructural model of PBS surely exists in blue-green algae and red algae. The function of this structural model of PBS was also discussed.