Differentiation between Phycobiliprotein and Colorless Linker Polypeptides by Fluorescence in the Presence of ZnSO(4)

Microcystis aeruginosa, a unicellular cyanobacterium, contains small phycobilisomes consisting of C-phycocyanin, allophycocyanin, and linker polypeptides. SDS-polyacrylamide gels of the phycobilisomes were examined for fluorescent bands before and after spraying with a solution of ZnSO₄, followed by Coomassie brilliant blue staining for protein. This procedure provides a rapid and sensitive method for detecting small amounts of phycobilin-containing polypeptides and distinguishing them from other tetrapyrrole-containing polypeptides and from `colorless' ones. Three polypeptide bands, in addition to the α and β phycobiliprotein subunits, have been detected under these conditions. An 85 kilodalton polypeptide was identified as a phycobiliprotein due to its enhanced fluorescence in the presence of ZnSO₄. The other polypeptides do not contain chromophores and are colorless. They are approximately 34.5 and 30 kilodaltons in size.