Allophycocyanin

Allophycocyanin is an accessory pigment to bacteriochlorophyll and is part of the phycobilin accessory pigment family, along with phycocyanin and phycoerythrin. All phycobilins, short for phycobiliproteins, are water soluble and therefore cannot exist within the membrane like carotenoids, but aggregate forming clusters that adhere to the membrane called phycobilisomes. Allophycocyanin absorbs red light, therefore emits blue, and is readily found in blue-green algae, now classified as Cyanobacteria, and red algae. Phycobilin pigments have fluorescent properties that are used in immunoassay kits. Allophycocyanin is from the Greek allo meaning "other," phyco meaning "algae" and cyanin is from the English "cyan." In flow cytometry, it is often abbreviated to APC.