phycobilin

(biliprotein) Any of the blue or red pigments found in the blue-green and red algae. Like the *carotenoids they are accessory pigments in photosynthesis, but unlike the chlorophylls and carotenoids they are water soluble. Structurally they are very similar to the porphyrin part of the *chlorophyll molecule , except that they contain no magnesium. The three classes of phycobilins are the *phycoerythrins , *phycocyanins , and allophycocyanins. See also phycobilisome.