Pigments phycobiliproteins

The phycobiliproteins are accessory photosynthetic pigments aggregated in cells as phycobilisomes that are attached to the thylakoid membrane of the chloroplast. The red phycobiliproteins (phycoerythrin) and the blue phycobiliprotein (phycocy-anin) are soluble in water and can serve as natural colorants in foods, cosmetics, and pharmaceuticals. Chemically, the phycobiliproteins are built from chro-mophores — bilins — that are open-chain tetrapyrroles covalently linked via thio-ether bonds to an apoprotein. ... 

Yaron, A. and Arad (Mails), S., Phycobiliproteins — blue and red natural pigments — for use in food and cosmetics, in Food Flavors, Ingredients and Composition Developments in Food Science, Vol. 32, Charalambous, G., Ed., Elsevier, London, 1993, 835. 

The participation of the phycobiliproteins in the absorption ofphotokinetically active light has been demonstrated above. Peaks of around 565 and 615 nm in the action spectra indicate the involvement of C-phycoerythrin andC-phycocanin. These pigments transfer energy to the reaction center of PS II and suggest the participation of the non-cyclic electron transport and coupled phosphorylation. 

There are three main classes of phycobiliproteins, differing in their protein structure, bilin content, and fluorescent properties. These are phycoerythrin, phycocyanin, and allo-phycocyanin (APC). There are two main forms of phycoerythrin proteins commonly in use B-phycoerythrin isolated from Porphyridium cruentum and R-phycoerythrin from Gastroclonium coulteri. There also are three main forms of pigments found in these proteins phycoerythrobilin, phycourobilin, and phycocya no bilin (Glazer, 1985). The relative content of these pigments in the phycobiliproteins determines their spectral properties. All of them,... 

The absorption spectra of the fractions obtained during the purification of the PSI particles are shown in Fig la. Both the sonicate and the original 40,000 xg supernatant showed a major peak at 620 nm due to soluble phycobiliproteins, which can be completely removed by batch chromatography on DE AE-cellulose. Thus, the A620/A676 ratio, which compares the absorption maxima of blue pigments to that of chlorophyll was 2.73 in the sonicate, 3.81 in the 40,000 xg supernatant, and only 0.27 in the DE-52 eluate. 

Figure 5-9. Structure of two phycobilins that act as important accessory pigments. Phycoerythrobilin has fewer double bonds in conjugation than phycocyanobilin, so its Xmax occurs at shorter wavelengths (Fig. 5-8). Phycobilins occur covalently bound to proteins that is, they are the chromo-phores for phycobiliproteins.

Phycobiliproteins, such as phycocyanin and phycoerythrin, are members of a family of fluorescent accessory, nonchlorophyll-based pigments found in cyanobacteria and eukaryotic algae. The phycobiliproteins have characteristic broad absorption profiles spanning 450-600 nm, emissions ranging 570-660 nm, and small stokes shifts see Fig. 3. The major structural subunits, phycoerythrobilin (PEB) or phycocyanobilin... 

---