Molecular Morphology of Cyanobacterial Phycobilisomes

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Abstract
Phycobilisomes were isolated from several cyanobacteria [Phormidium persicinum, Tolypothrix tenuis, Fremyella diplosiphon, Phormidium luridum, Microcystis aeruginosa and Aphanizomenon flos-aquae] following cell lysis with Triton X-100. They were purified by phosphate precipitation and hydrophobic-interaction chromatography. Their phycobiliprotein compositions were quantitatively determined by application of sets of simultaneous absorbance equations to gel chromatographic separations of the chromoproteins. Phycobilisomes purified from several cyanobacteria had characteristic elution times on agarose gel chromatography. Combining EM observations of phycobilisome structure, phycobiliprotein composition and agarose gel chromatography, estimates of MW permitted the calculation of many details of phycobilisome molecular structure. Complementary chromatic adaptation resulted in a change of phycobilisome composition and structure. The polypeptide compositions of phycobilisomes were examined by sodium dodecyl sulfate[SDS]-agarose gel chromatography and SDS-polyacrylamide gel electrophoresis. The phycobilisomes were composed of phycobilipeptides derived from the constituent phycobiliproteins. Higher MW phycobilipeptide aggregates were also present. The dominant forces responsible for the maintenance of phycobilisome structure are hydrophobic interactions.