Differentiation between Phycobiliprotein and Colorless Linker Polypeptides by Fluorescence in the Presence of ZnSO4

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Abstract
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 amount of phycobilin-containing polypeptides and distinguishing them from other tetrapyrrole-containing polypeptides and from ''colorless'' ones. Three polypeptide bands, in addition to the .alpha. and .beta. 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.