Phycocyanobilin is a blue phycobilin, i.e., a

tetrapyrrole Tetrapyrroles are a class of chemical compounds that contain four pyrrole or pyrrole-like rings. The pyrrole/pyrrole derivatives are linked by ( =- or -- units), in either a linear or a cyclic fashion. Pyrroles are a five-atom ring with four car ...

chromophore found in

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

and in the chloroplasts of red algae,

glaucophyte The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of unicellular algae found in freshwater and moist terrestrial environments, less common today than they were during the Proterozoic. The stated number of spe ...

s, and some

cryptomonad The cryptomonads (or cryptophytes) are a group of algae, most of which have plastids. They are common in freshwater, and also occur in marine and brackish habitats. Each cell is around 10–50 μm in size and flattened in shape, with an anteri ...

s. Phycocyanobilin is present only in the phycobiliproteins

allophycocyanin Allophycocyanin ("other algal blue protein"; from Greek: '' (allos)'' meaning "other", '' (phykos)'' meaning “alga”, and '' (kyanos)'' meaning "blue") is a protein from the light-harvesting phycobiliprotein family, along with phycocyanin, phyco ...

and

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 w ...

, of which it is the terminal acceptor of energy. It is covalently linked to these phycobiliproteins by a

thioether In organic chemistry, an organic sulfide (British English sulphide) or thioether is an organosulfur functional group with the connectivity as shown on right. Like many other sulfur-containing compounds, volatile sulfides have foul odors. A su ...

bond. Phycocyanobilin, PCB, has the ability to bind to human serum albumin, HSA, protein found mainly in the blood of humans. This PCB-HCA complex benefits the structure of HSA, increasing the thermal stability of HSA, as well as increasing its ability to prevent against proteolytic activity of other proteins.

References

Further reading