Phycocyanin is a pigment

Pigment

A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...

 from the light-harvesting phycobiliprotein

Phycobiliprotein

Phycobiliproteins are water-soluble proteins present in cyanobacteria and certain algae that capture light energy, which is then passed on to chlorophylls during photosynthesis. Phycobiliproteins are formed of a complex between proteins and covalently bound phycobilins that act as chromophores...

 family, along with allophycocyanin

Allophycocyanin

Allophycocyanin is a protein from the light-harvesting phycobiliprotein family, along with phycocyanin, phycoerythrin and phycoerythrocyanin. It is an accessory pigment to chlorophyll...

 and phycoerythrin

Phycoerythrin

Phycoerythrin is a red protein from the light-harvesting phycobiliprotein family, present in cyanobacteria, red algae and cryptomonads.Like all phycobiliproteins, phycoerythrin is composed of a protein part, organised in a hexameric structure of alpha and beta chains, covalently binding...

. It is an accessory pigment

Accessory pigment

Accessory pigments are light-absorbing compounds, found in photosynthetic organisms, that work in conjunction with chlorophyll a. They include other forms of this pigment, such as chlorophyll b in green algal and higher plant antennae, while other algae may contain chlorophyll c or d...

 to chlorophyll

Chlorophyll

Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...

. All phycobiliproteins are water-soluble and therefore cannot exist within the membrane as do carotenoids, but aggregate forming clusters that adhere to the membrane called phycobilisome

Phycobilisome

Phycobilisomes are light harvesting antennae of photosystem II in cyanobacteria, red algae and glaucophytes.- General structure :Phycobilisomes are protein complexes anchored to thylakoid membranes. They are made of stacks of chromophorylated proteins, the phycobiliproteins, and their associated...

s. Phycocyanin is a characteristic light blue colour, absorbing orange and red light, particularly near 620 nm (depending on which specific type it is), and emits fluorescence at about 650 nm (also depending on which type it is). Allophycocyanin absorbs and emits at longer wavelengths than Phycocyanin C or Phycocyanin R. Phycocyanins are found in Cyanobacteria (previously called blue-green algae). Phycobiliproteins have fluorescent properties that are used in immunoassay

Immunoassay

An immunoassay is a biochemical test that measures the presence or concentration of a substance in solutions that frequently contain a complex mixture of substances. Analytes in biological liquids such as serum or urine are frequently assayed using immunoassay methods...

 kits. Phycocyanin is from the Greek phyco meaning “algae

Algae

Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

” and cyanin is from the English word “cyan

Cyan

Cyan from , transliterated: kýanos, meaning "dark blue substance") may be used as the name of any of a number of colors in the blue/green range of the spectrum. In reference to the visible spectrum cyan is used to refer to the color obtained by mixing equal amounts of green and blue light or the...

", which conventionally means a shade of blue-green (close to "aqua") and is derived from the Greek “kyanos" which means a somewhat different color: "dark blue." The product phycocyanin, produced by Aphanizomenon flos-aquae

Aphanizomenon flos-aquae

Aphanizomenon flos-aquae is a freshwater species of cyanobacteria. Cyanobacteria are an ancient clade of bacterial microphyte, part of the cyanobacteria phylum.AFA as a species has both toxic and nontoxic forms...

 and Spirulina

Spirulina

Spirulina may refer to:* Spirulina , a health-food supplement* Spirulina , a cyanobacterium group* Ochthephila spirulina, species of gastropod in the Hygromiidae family...

, is used in the food and beverage industry as a natural coloring agent 'Lina Blue' and is found in sweets and ice cream.

The phycobiliproteins are made of subunits having a protein backbone to which a linear tetrapyrrole chromophores are bound.