Phycoerythrin
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Phycoerythrin is a red protein from the light-harvesting phycobiliprotein family, isolated from cyanobacteria, red algae and cryptomonads.
A strong absorption peak exists at about 566 nm, and a strong emission peak exists at 575 ± 10 nm. (i.e. phycoerythrin absorbs green light and emits red light.)
Like all phycobiliproteins, phycoerythrin contains chromophores called phycobilins (e.g. phycoerythrobilin, phycourobilin).
In some photosynthetic organisms, phycoerythrin is an accessory pigment to the main light-absorbing chlorophyll pigments responsible for photosynthesis. The light energy is captured by phycoerythrin and is then passed on to chlorophyll.
R-Phycoerythrin is useful in the laboratory as a fluorescence-based indicator for the presence of cyanobacteria and for labeling antibodies in a technique called immunofluorescence, among other applications. There are also other types of phycoerythrins, such as B-Phycoerythrin, which has a slightly different spectral characteristic. B-Phycoerythrin abosorbs strongly at about 545 nm and emits strongly at 572 nm instead and could be better suited for some instruments. B-Phycoerythrin may also be less "sticky" than R-Phycoerythrin and contributes less to background signal due to non-specific binding in certain applications.
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