Phycoerythrin Avidin D is used to fluorescently label biotinylated antibodies or other biotiny-lated molecules in flow cytometry procedures. However, because of size and photobleaching characteristics it has limited use in tissue staining applications. R-phycoerythrin which is isolated from Gastroclonium coulteri, a marine alga, is one of a family of proteins called phycobiliproteins. These proteins are part of the light-harvesting system of cyanobacteria and red algae and for that reason contain a considerable number of chromophores covalently bound to the peptide backbone. When purified, the phycobiliproteins are highly fluorescent, with each protein molecule being up to twenty times as intense as a fluorescein molecule. The fluorescence is also stable over a wide range of conditions. R-phycoerythrin was selected for this conjugate because of its high extinction coefficient and quantum yield as well as its useful absorption and emission profiles. It has a broad absorption range from 450 nm to 570 nm and a maximum emission at 574 nm. These properties are unaffected by the method that has been used to couple the protein to Avidin D. This product can be used in double labeling applications in conjunction with fluorescein.
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