fycocyanine

Fycocyanine is a term that occasionally appears in reference works as a variant spelling of phycocyanin, a blue pigment–protein complex used by cyanobacteria and red algae for light harvesting. In standard nomenclature, the pigment–protein is called phycocyanin. Phycocyanin is a phycobiliprotein composed of α and β subunits bound to phycocyanobilin chromophores, and it is water-soluble, forming oligomeric assemblies such as trimers and hexamers.

Spectral properties of phycocyanin include light absorption around 620–630 nm and fluorescence emission near 640–660 nm when excited at approximately 590–650 nm. Its bright blue color and distinct fluorescence make it useful as a natural marker in biochemical assays. Phycocyanin occurs naturally in many cyanobacteria, including Spirulina, and in some red algae, where it is part of the light-harvesting antennae known as phycobilisomes.

Applications of phycocyanin span research and industry. It is used as a fluorescent label in microscopy, flow cytometry, and immunoassays, taking advantage of its strong fluorescence and relatively high stability in water. It has also been employed as a natural blue colorant in foods and cosmetics in certain markets, with purity and regulatory approval dependent on jurisdiction.

Isolation and purification typically start with aqueous extraction from algal biomass, followed by ammonium sulfate precipitation and chromatographic techniques to obtain high-purity phycocyanin. Stability is influenced by pH, temperature, and ionic strength, with degradation occurring under extreme conditions.