Phycoerythrin
![Phycobiliproteins (like phycoerythrin) usually form rods of stacked disks in phycobilisomes.[3]](/Images/godic/202502/02/Phycobilisome_structure2428.jpg")
![The crystal structure of B-phycoerythrin from red algae Porphyridium cruentum (PDB ID: 3V57 [5][6][7]). The asymmetric unit (αβ)2 on the left and assumed biological molecule (αβ)3. It contains phycoerythrobilin, N-methyl asparagine and SO42−.](/Images/godic/202502/02/B-phycoerythrin_3V572428.png")
![Phycoerythrobilin is the typical chromophore in phycoerythrin. It is similar to porphyrin of chlorophyll for example, but tetrapyrrole is linear, not closed into ring with metal ion in the middle.](/Images/godic/202502/02/Phycoerythrobilin2.svg2428.png")
![The red algae Gracilaria contains R-phycoerythrin.](/Images/godic/202502/02/Gracilaria22428.JPG")
Phycoerythrin (PE) is a red protein-pigment complex from the light-harvesting phycobiliprotein family, present in red algae and cryptophytes, accessory to the main chlorophyll pigments responsible for photosynthesis.
Like all phycobiliproteins, it is composed of a protein part covalently binding chromophores called phycobilins. In the phycoerythrin family, the most known phycobilins are: phycoerythrobilin, the typical phycoerythrin acceptor chromophore, and sometimes phycourobilin. Phycoerythrins are composed of (αβ) monomers, usually organised in a disk-shaped trimer (αβ)3 or hexamer (αβ)6 (second one is the functional unit of the antenna rods). These typical complexes contain also third type of subunit, the γ chain.