Phycoerythrobilin

Phycoerythrobilin is a bilin pigment that is found in red algae and cyanobacteria. It is a photosynthetic pigment that absorbs light in the green region of the electromagnetic spectrum, and is responsible for the red color of red algae and some cyanobacteria.

Structure and Properties

Phycoerythrobilin is a linear tetrapyrrole compound, similar in structure to the heme group found in hemoglobin. It consists of four pyrrole rings linked by methine bridges, with two propionate side chains. The molecule is planar, which allows it to effectively absorb light.

The absorption maximum of phycoerythrobilin is around 550 nm, in the green region of the spectrum. This allows organisms that contain this pigment to perform photosynthesis using light that is not absorbed by chlorophyll, giving them a competitive advantage in certain environments.

Biosynthesis

Phycoerythrobilin is synthesized from biliverdin, a product of heme degradation. The conversion of biliverdin to phycoerythrobilin is catalyzed by the enzyme phycoerythrobilin synthase, which is found in the plastids of red algae and cyanobacteria.

Function

In red algae and cyanobacteria, phycoerythrobilin is bound to phycobiliproteins, forming phycobilisomes. These are large protein complexes that are attached to the thylakoid membrane, and play a crucial role in light harvesting for photosynthesis. The energy absorbed by phycoerythrobilin is transferred to chlorophyll via energy transfer processes, allowing the organism to utilize light that would otherwise be wasted.

See Also

• Phycocyanobilin
• Phycoerythrin
• Phycobilisome
• Photosynthesis

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