- Phycobilin
Phycobilins (from Greek: "polytonic|φύκος (phykos)" meaning "alga", and from
Latin : "bilis" meaning "bile") arechromophore s (light-capturing molecules) found incyanobacteria and in thechloroplast s ofred algae ,glaucophyte s and somecryptomonad s (though not ingreen algae and higherplant s). They are unique among the photosynthetic pigments in that they are bonded to certain water-solubleprotein s, known asphycobiliprotein s. Phycobiliproteins then pass the light energy tochlorophyll s forphotosynthesis .The phycobilins are especially efficient at absorbing red, orange, yellow and green light, wavelengths which are not well absorbed by chlorophyll "a". Organisms growing in shallow waters tend to contain phycobilins that can capture yellow/red light, while those at greater depth often contain more of the phycobilins that can capture green light, which is relatively more abundant there.
The phycobilins fluoresce at a particular wavelength, and are therefore often used in research as chemical tags, e.g. by binding phycobiliproteins to antibodies in a technique known as
immunofluorescence .Types
There are four types of phycobilins:
#Phycoerythrobilin , which is red
#Phycourobilin , which is orange
#Phycoviolobilin (also known as phycobiliviolin) found inphycoerythrocyanin
#Phycocyanobilin (also known as phycobiliverdin), which is blue.They can be found in different combinations attached to phycobiliproteins to confer specific spectroscopic properties.
tructural relation to other molecules
Chemically, phycobilins consist of an open chain of four
pyrrole rings ("tetrapyrrole ") and are structurally similar to thebile pigmentbilirubin , which explains the name. (Bilirubin's conformation is also affected by light, a fact used for thephototherapy ofjaundice d newborns.)Phycobilins are also closely related to the chromophores of the light-detecting plant pigmentphytochrome which also consist of an open chain of four pyrroles.Chlorophyll s are composed of four pyrroles as well, but there the pyrroles are arranged in a ring and contain a metal atom in the center.References
* O'Carra P, Murphy RF, Killilea SD. "The native forms of the phycobilin chromophores of algal biliproteins. A clarification." Biochem J. 1980 May 1;187(2):303-9. PMID 7396851
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