Light-harvesting complex carotenoid molecule

Figure 12.17 Computer-generated diagram of the stmcture of light-harvesting complex LH2 from Rhodopseudomonas acidophila. Nine a chains (gray) and nine p chains Bight blue) form two rings of transmembrane helices between which are bound nine carotenoids (yellow) and 27 bacteriochlorophyll molecules (red, green and dark blue). (Courtesy of M.Z. Papiz.)...

Eukaryotic plants and cyanobacteria. Photosynthetic dinoflagellates, which make up much of the marine plankton, use both carotenoids and chlorophyll in light-harvesting complexes. The carotenoid peridinin (Fig. 23-29), which absorbs blue-green in the 470- to 550-nm range, predominates. The LH complex of Amphidinium carterae consists of a 30.2-kDA protein that forms a cavity into which eight molecules of peridinin but only two of chlorophyll a (Chi a) and two molecules of a galactolipid are bound (Fig. 23-29).268... 

Fignre 19.30. Stmctnre of a Light-Harvesting Complex. Eight polypeptides, each of which binds three chlorophyll % molecules (green) and a carotenoid molecule (red), surround a central cavity that contains the reaction center. 

In photosynthetically active chloroplasts, the carotenoids are found as part of photosynthetic pigment-protein complexes (PPCs) in the thylakoid membranes. The core complex, CCI, contains one /3-carotene molecule per 40 chlorophyll a, whereas the light-harvesting complex LHCI is associated with lutein, violaxanthin, and neoxanthin. /3-Carotene is also located in CCII, ° while LHCII contains xanthophylls." The separation, identification, and nomenclature of the PPCs has been discussed in detail in several recent reviews. ... 

---