Phycobiliproteins

Phycobiliproteins are water-soluble, light-harvesting proteins that are highly fluorescent due to the incorporation of tetrapyrrole chromophores. They are isolated from cyanobacteria and eukaryotic algae. Phycobiliproteins hold the record for the largest number of photons emitted before bleaching – they are one of the most sensitive fluorescent reporters known. They combine extremely high extinction coefficients and quantum yields close to unity (see below). Because of their high sensitivity, phycobiliprotein-labeled antibodies are used in fluorescence applications such as flow cytometry and immuno-blotting/immuno-staining.

The main classes of phycobiliproteins are: Allophycocyanin, R-Phycocyanin, B-Phycoerythrin, R-Phycoerythrin:
 

They are also used as energy transfer donors in tandem-constructs for multi-color analysis in flow cytometry applications.