Phycoerythrobilin

Chemical structure

Phycoerythrobilin is a tetrapyrrole formed in nature by the catabolism of heme B via biliverdin. Two geometric isomers of the compound have been reported, which differ only in the configuration of one sidechain. The stereochemistry of the compounds were confirmed by total synthesis of their methyl esters.

Biosynthesis

(E) and (Z)-phycoerythrobilin are products of porphyrin biosynthesis beyond heme B. They arise from its oxidation which cleaves the macrocyclic ring, giving biliverdin:

Biliverdin is then reduced to give either the (E) or (Z) isomers of phycoerythrobilin, for example by phycoerythrobilin synthase:

There is evidence that in some organisms it is the (3Z) form that is produced first and that this is converted into the (3E) isomer.

Biological role

Phycoerythrobilins are components of phycobilisome protein complexes, the light-harvesting antennae that transmit the energy of photons to photosystem II and photosystem I in cyanobacteria and in the chloroplasts of red algae and glaucophytes. The absorption spectrum of phycoerythrobilins in the 500–650 nm range where chlorophyll absorbs poorly allows organisms such as Galdieria sulphuraria which use them to be more efficient.

The tetrapyrrole is covalently attached to the phycobiliprotein through a bond between the sulfur of a cysteine amino-acid and the (3E) or (3Z) ring-C=CCH3 sidechain, as a thioether.

Uses

Phycoerythrobilins, in the form of phycobiliproteins, are widely used in foodstuffs and cosmetics as colourants. They are mainly obtained from Spirulina species.

References

References

1. (1967). "Structure of phycoerythrobilin". [[Journal of the American Chemical Society]].
2. (2023). "Cyanobacterial Biotechnology in the 21st Century". Springer Nature.
3. Compare [[PubChem]] [https://pubchem.ncbi.nlm.nih.gov/compound/20057005 entry for (3''E'') isomer] with [https://pubchem.ncbi.nlm.nih.gov/compound/11953875 entry for (3''Z'') isomer]
4. (1978). "Synthesis of bile pigments. 9. Chemical total synthesis of (+)-(2R,16R)- and (+)-(2S,16R)-phycoerythrobilin dimethyl ester". Journal of the American Chemical Society.
5. (2008). "Efficient Phage-Mediated Pigment Biosynthesis in Oceanic Cyanobacteria". Current Biology.
6. (2008). "Phycoerythrobilin Synthase (PebS) of a Marine Virus". Journal of Biological Chemistry.
7. (1991). "Biosynthesis of phycobilins. 3(Z)-phycoerythrobilin and 3(Z)-phycocyanobilin are intermediates in the formation of 3(E)-phycocyanobilin from biliverdin IX alpha". Journal of Biological Chemistry.
8. (2022). "Core and rod structures of a thermophilic cyanobacterial light-harvesting phycobilisome". Nature Communications.
9. (2015). "Structural organization of an intact phycobilisome and its association with photosystem II". Cell Research.
10. (2026). "Phycocyanobilin biosynthesis in ''Galdieria sulphuraria'' requires isomerization of phycoerythrobilin synthesized by bilin reductases". The FEBS Journal.
11. (2011). "Spectroscopic parameters of phycoerythrobilin and phycourobilin on phycoerythrin from Gracilaria chilensis". Journal of Photochemistry and Photobiology A: Chemistry.
12. (2023). "Phycobiliproteins from algae: Current updates in sustainable production and applications in food and health". Food Research International.