Фикоэритрин: Қызыл пигмент және оның қасиеттері

Phycoerythrin (PE) is a red protein pigment complex from the light harvesting phycobiliprotein family, present in cyanobacteria, red algae

Like all phycobiliproteins, it is composed of a protein part covalently binding chromophores called phycobilins. In the phycoerythrin family, the most known phycobilins are: phycoerythrobilin, the typical phycoerythrin acceptor chromophore. Phycoerythrobilin is a linear tetrapyrrole molecule found in cyanobacteria, red algae, and cryptomonads. Together with other bilins such as phycocyanobilin it serves as a light harvesting pigment in the photosynthetic light harvesting structures of cyanobacteria called phycobilisomes. Phycoerythrins are composed of (αβ) monomers, usually organised in a disk shaped trimer (αβ)3 or hexamer (αβ)6 (second one is the functional unit of the antenna rods). These typical complexes also contain a third type of subunit, the γ chain. Phycoerythrin is an accessory pigment to the main chlorophyll pigments responsible for photosynthesis. The light energy is captured by phycoerythrin and is then passed on to the reaction centre chlorophyll pair, most of the time via the phycobiliproteins phycocyanin and allophycocyanin.

Absorption peaks in the visible light spectrum are measured at 495 and 545/566 nm, depending on the chromophores bound and the considered organism. A strong emission peak exists at 575 ± 10 nm. (Phycoerythrin absorbs slightly blue green/yellowish light and emits slightly orange yellow light.) Property Value Absorption maximum 565 nm Additional Absorption peak 498 nm Emission maximum 573 nm Extinction Coefficient (ε) 1.96e6 Quantum Yield (QY) 0.84 Brightness (ε × QY) 1.65e6

PEB and DBV bilins in PE545 absorb in the green spectral region too, with maxima at 545 and 569 nm respectively. The fluorescence emission maximum is at 580 nm.

As mentioned above, phycoerythrin can be found in a variety of algal species. As such, there can be variation in the efficiency of absorbance and emission of light required for facilitation of photosynthesis. This could be a result of the depth in the water column that a specific alga typically resides and a consequent need for greater or less efficiency of the accessory pigments. With advances in imaging and detection technology which can avoid rapid photobleaching, protein fluorophores have become a viable and powerful tool for researchers in fields such as microscopy, microarray analysis and Western blotting. In light of this, it may be beneficial for researchers to screen these variable R phycoerythrins to determine which one is most appropriate for their particular application. Even a small increase in fluorescent efficiency could reduce background noise and lower the rate of false negative results.

R Phycoerythrin (also known as PE or R PE) is useful in the laboratory as a fluorescence based indicator for the presence of cyanobacteria and for labeling antibodies, most often for flow cytometry. Its also used in microarray assays, ELISAs, and other applications that require high sensitivity but not photostability. Its use is limited in immunofluorescence microscopy due to its rapid photobleaching characteristics. There are also other types of phycoerythrins, such as B phycoerythrin, which have slightly different spectral properties. B Phycoerythrin absorbs strongly at about 545 nm (slightly yellowish green) and emits strongly at 572 nm (yellow) instead and could be better suited for some instruments. B Phycoerythrin may also be less "sticky" than R phycoerythrin and contributes less to background signal due to nonspecific binding in certain applications. However, R PE is much more commonly available as an antibody conjugate. Phycoerythrin (PE, λA max = 540–570 nm; λF max = 575–590 nm)