Phycoerythrobilins

Phycoerythrobilins are a class of tetrapyrrole pigments found in certain cyanobacteria and red algae. They are structurally related to phycobilins, which are accessory photosynthetic pigments. Specifically, phycoerythrobilins are chromophores found within the phycoerythrin proteins. Phycoerythrin is a light-harvesting pigment that absorbs light in the green and yellow regions of the visible spectrum, wavelengths that penetrate deeper into water than red light. This adaptation allows photosynthetic organisms in aquatic environments to utilize a broader range of light for photosynthesis.

The molecular structure of phycoerythrobilin features an open-chain tetrapyrrole arrangement, distinguishing it from cyclic porphyrins like chlorophyll. The specific arrangement of double bonds and conjugated systems within the molecule is responsible for its characteristic absorption spectrum. In the context of phycoerythrin, phycoerythrobilin molecules are covalently attached to the protein scaffold, typically through thioether linkages. This close association with the protein allows for efficient energy transfer from the absorbed light to the reaction centers of photosynthesis. The presence and abundance of phycoerythrobilins contribute to the vibrant red or orange coloration observed in some cyanobacteria and red algae.