fykobilinimolekyyleistä

Phycobilins are a group of light-harvesting protein pigments found in cyanobacteria, red algae, and some other organisms. They are related to bilirubin and other bile pigments, hence the name "phycobilin" which translates to "algae bile." Unlike chlorophylls, phycobilins do not contain magnesium and have an open-chain tetrapyrrole structure. Their primary function is to absorb light energy, particularly in spectral regions where chlorophyll is less efficient, and transfer this energy to reaction centers for photosynthesis.

The most well-known phycobilins are phycocyanin and phycoerythrin. Phycocyanin typically absorbs orange-red light, while phycoerythrin absorbs green-yellow light. These pigments are organized into large macromolecular complexes called phycobilisomes, which are attached to the thylakoid membranes within the photosynthetic cell. Phycobilisomes act as efficient light-gathering antennae, channeling absorbed energy towards chlorophyll molecules in the photosystems. The specific types and proportions of phycobilins can vary depending on the organism and its light environment, allowing for adaptation to different light conditions. For example, organisms living in deeper water often have higher amounts of phycoerythrin to capture the green light that penetrates to those depths. Phycobilins are also responsible for the characteristic colors of many algae, such as the blue of phycocyanin in cyanobacteria and the red of phycoerythrin in red algae.