Characterization of cyanobacterial phycobilisomes in zwitterionic detergents

Properties of cyanobacterial phycobilisomes (from Synechococcus spp. 6301 and 6312 and Synechocystis sp. 6701) prepared in the presence of two different zwitterionic detergents were compared to those of phycobilisomes detached from membranes with the nonionic detergent Triton X-100 and then freed from Triton by sedimentation through high-salt sucrose density gradients. The absorption spectra, polypeptide composition, and ultrastructure of phycobilisomes were independent of the detergent used during the preparation. Phycobilisomes from certain cyanobacteria aggregated in the absence of detergent. Such aggregation was not seen in preparations containing zwitterionic detergents. Aggregation of phycobilisomes led to a partial quenching of their fluorescence. Electron microscopy showed the three types of phycobilisomes to have a hemi-disc appearance, although their detailed structures were quite different.