Phycocyanin is a pigment from the light-harvesting phycobiliprotein family, along with allophycocyanin and phycoerythrin. It is an accessory pigment to chlorophyll. 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 phycobilisomes. 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 kits. Phycocyanin is from the Greek phyco meaning “algae” and cyanin is from the English word “cyan", 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 and Spirulina, 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.
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