Phycoerythrobilin

Phycoerythrobilin is a linear tetrapyrrole bilin chromophore found in the phycobiliproteins of cyanobacteria and red algae. It is one of the bilin pigments that extend light absorption of the photosynthetic antennae into the green–yellow region, contributing to the red coloration of phycoerythrin when bound to proteins.

In biosynthesis, phycoerythrobilin is produced from biliverdin IXα through bilin reductase–mediated reactions and is then covalently attached to specific apoproteins of phycobiliproteins by lyase enzymes to form functional chromophore-protein complexes.

When bound to phycobiliproteins, phycoerythrobilin absorbs light in the green-yellow part of the spectrum and emits fluorescence around 575 nm. Its bright fluorescence and spectral tunability depending on the protein scaffold make phycobiliproteins useful as fluorescent probes.

Phycoerythrobilin-containing phycobiliproteins, such as phycoerythrin, are prominent in cyanobacteria and red algae and aid in light harvesting under greenish light conditions. They supplement chlorophyll-based photosystems by capturing wavelengths that chlorophyll a poorly absorbs.

Phycobiliproteins containing phycoerythrobilin are widely used in biochemical assays and fluorescence-based techniques, for example as fluorescent labels in flow cytometry and microscopy.