Phycocyanin

Phycocyanin is a pigment-protein complex from the light-harvesting phycobiliprotein family, along with allophycocyanin and phycoerythrin. It is an accessory pigment to chlorophyll. All phycobiliproteins are water-soluble, so they cannot exist within the membrane like carotenoids can. Instead, phycobiliproteins aggregate to form clusters that adhere to the membrane called phycobilisomes.

Phycocyanin is a characteristic light blue color, 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 (also called blue-green algae).

Structure

Phycocyanin is a complex of proteins and pigments. It is composed of two subunits: alpha and beta, which are usually present in equal amounts. Each subunit has a single phycocyanobilin chromophore. The protein part of the molecule is globular, composed of a single polypeptide chain.

Function

Phycocyanin plays a key role in the light-harvesting process of photosynthesis. It absorbs orange and red light, which is then passed on to chlorophyll for the actual photosynthetic process. This makes phycocyanin an accessory pigment, helping to broaden the range of light that a photosynthetic organism can use.

Applications

Phycocyanin has several applications, particularly in the food and cosmetic industries. It is used as a natural blue colorant in certain food and drink products. It is also used in cosmetics for its antioxidant and anti-inflammatory properties.

See also

• Chlorophyll
• Photosynthesis
• Cyanobacteria

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