Phycobilisomes

Phycobilisomes are typically attached to the stromal surface of thylakoid membranes in prokaryotes (Cyanobacteria) and eukaryotes (cryptomonads, red algae, cyanelles).[rev]

Four main groups of chromophore have been characterized from red algae and cyanobacteria,
and five additional types from cryptomonads:
1. phycoerythrobilin,
2. phycocyanobilin,
3. phycourobilin, and
4. phycobiliviolin
The pigments are covalently bound by thioether linkages to their cognate proteins.

The Cyanobacteria possess photosynthetic thylakoid membranes studded with phycobilin-containing phycobilisomes (PBSs).

Marine Synechococcus spp. possess one of the most sophisticated antenna complexes found in the Cyanobacteria. It is proposed that, homologous with freshwater Cyanobacteria, PBSs possess six rods radiating around an allophycocyanin core, and that, at low light, rods comprise a single phycocyanin basal hexamer (disk), two phycoerythrin I disks, and three phycoerythrin II disks maintained by linker polypeptides (figure). Two new linkers have been characterized – MpeC and MpeD – that are involved in the binding of phycoerythrin (PE) disks. MpeC binds the middle PEII disk to the proximal disk, and MpeD binds the distal PEI disk to the proximal PEII disk. Phycobiliproteins APC, PC, PEI and PEII are colored pigments that enable these antenna complexes to capture and transfer photons of various energies to the reaction centers.[s]

: phycobilisomes Rhodophyta : phycobilisomes phycoerythrin : tem chloroplast thylakoid phycobilisomes : tem chloroplast Rhodella : tem phycobilisomes thylakoids Rhodella : R-phycoerythrin R-PE:cyanin-5 allophycocyanin fluorochromes & absorbance wavelength scans for the fluorochromes : figure PBS :

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