Phycobilisome isolation and C-phycocyanin purification from the cyanobacterium Aphanizomenon gracile

Cyanobacterial phycobilisomes are made up from phycobiliproteins held together by linker proteins. Incident photons are absorbed by the phycobiliproteins that carry linear tetrapyrrole chromophores with extended conjugated bond systems. The chemical structure of the chromophores also bestows the phycobiliproteins with excellent radical scavenging and antioxidant properties and phycobiliproteins have pharmaceutical value as such. We purified and characterized the phycobilisome and its major protein constituent C-phycocyanin from the freshwater filamentous cyanobacterium Aphanizomenon gracile. Isolated phycobilisomes were shown to be intact and contained the phycobiliproteins allophyco-cyanin and C-phycocyanin, but not phycoerythrin, together with the classic set of linker proteins. C-phycocyanin could be easily purified and was of analytical grade with spectral characteristics similar to that of other cyanobacterial species. To our best knowledge, this is the first study to report the purification and characterization of the Aphanizomenon gracile phycobilisome and C-phycocyanin.