Rphycoerythrin

R-phycoerythrin (R-PE) is a phycobiliprotein pigment-protein complex that functions as part of the light-harvesting system in red algae and some cyanobacteria. It belongs to the phycobiliprotein family, which captures light energy and transfers it to chlorophyll for photosynthesis. R-PE is among the most intensely fluorescent natural proteins and is widely used as a fluorescent label in biomedical research.

Structurally, R-PE is a large oligomeric complex composed of alpha and beta subunits arranged into trimers and higher-order aggregates. It carries multiple chromophore groups, primarily phycoerythrobilin and related bilin chromophores, covalently attached to the polypeptide chains by lyases. This arrangement yields high molar absorptivity and brightness.

Spectral properties of R-PE include absorption maxima around 495, 545, and 565 nm, with emission typically around 575–580 nm. This combination produces strong fluorescence that can be excited by common laser lines, making R-PE a popular choice for fluorescence-based detection.

Applications of R-PE include use as a fluorescent label in flow cytometry, enzyme-linked immunosorbent assays (ELISAs), Western blotting, and immunohistochemistry. It is often conjugated to antibodies or other targeting molecules to enable sensitive detection, and its high brightness helps distinguish signals in multiplex assays.

Production and purification are carried out commercially, typically by extraction from red algae (such as species in the Porphyra/Griffithsia group) or by recombinant expression in microbial hosts to ensure consistent quality. Purified R-PE is then subjected to standard protein chromatography for isolation. Stability is improved by protecting from light and storing under refrigerated conditions. See also phycobiliproteins and phycoerythrin.