Phycobiliprotein pigments

All phycobiliproteins carry at least one linear tetrapyrrole chromophore. The chromophores impart to the proteins their characteristic visible absorption properties. 4 chemically distinct chromophores are known to occur among cyanobacterial biliproteins :- phycocyanobilin, phycoerythrobilin, phycourobilin and a bilividin-type chromophore. 2 distinct sub-populations distinguished on the basis of the predominant chromophore associated with phycoerythrin a) phycourobilin-rich strains - characteristic of the open ocean b) low phycourobilin-containing strains associated with shelf waters