ficobilinas

Ficobilinas, also known as phycobilins, are a family of water-soluble linear tetrapyrrole pigments found mainly in cyanobacteria, red algae (rhodophyta) and some glaucophytes. They form part of the light-harvesting antennae called phycobiliproteins, which assemble into phycobilisomes attached to the thylakoid membranes. The principal phycobiliproteins are phycoerythrin, phycocyanin and allophycocyanin, each carrying covalently bound chromophores that define their spectral properties (phycoerythrobilin in phycoerythrin, phycocyanobilin in phycocyanin, allophycocyanobilin in allophycocyanin).

Ficobilinas broaden the usable light spectrum because they absorb wavelengths that chlorophyll a does not efficiently use, enabling photosynthesis in environments with filtered or limited light. Absorption maxima vary: phycoerythrin roughly 495–570 nm, phycocyanin roughly 600–650 nm, and allophycocyanin roughly 650–660 nm; energy captured by these pigments is transferred to chlorophyll a within the photosystems via the phycobilisome.

Biosynthesis involves the conversion of biliverdin IXα to the various phycobilin chromophores by bilin reductases, followed by covalent attachment to cysteine residues of phycobiliprotein subunits through lyases. Ficobilinas are essential for efficient light capture in aquatic photosynthesis and have applications in biotechnology as fluorescent probes, with phycoerythrin and phycocyanin widely used as fluorescent labels in assays and imaging.