Carotenoids functional role

The results of this study demonstrate that the antenna and the reaction center of R rubrum differ in then-specificities of carotenoid binding. Thus, the microorganism follows in this respect the pattern of other related phototrophic bacteria (Cogdell and Thomber, 1979 Cogdell et al., 1976). Such difference suggests strongly that the functional role of the carotenoid in each type of photosynthetic complex has differential aspects of importance sufficient to impose distinctive structural requirements. The available information on... 

The biochemical and photochemical approaches described thus far have allowed significant advances in our understanding of the structural and functional roles of carotenoids in photosynthesis and photosystem assembly and have laid the groundwork for many of the most widely accepted theories in the field. The continued development and use of these approaches will be of central importance to research... 

More than 55,000 terpenes have been isolated, and this number has almost doubled each decade [9, 10]. The diverse functional roles of many terpenoids have been characterized. Eucalyptus, conifer wood, balm trees, cinnamon, cloves, citms fruits, coriander, ginger, lavender, lemongrass, lilies, carnation, caraway, peppermint species, roses, rosemary, sage, thyme, violet, and many other plants or parts of those (stems, leaves, blossoms, roots, rhizomes, fruits, seed) are well known to smell pleasantly, to taste spicy, or to exhibit specific pharmacological activities which chiefly are attributed to the presence of terpenes. Also, terpenes have shown to be useful as hormones (gibbereUins), photosynthetic pigments (phytol, carotenoids). 

In plants, carotenoids are held in the chloroplasts, where they are found as complexes formed through non-covalent binding with proteins. Within the chloroplasts, carotenoids have important functional roles as accessory lightharvesting pigments and as photo-protective agents. 

In animals, the major function of carotenoids is as a precursor to the formation of vitamin A. Carotenoids with provitamin A activity are essential components of the human diet, and there is considerable evidence that they are absorbed through the diet and often metabohzed into other compounds. Beyond their important role as a source of vitamin A for humans, dietary carotenoids, including those that are not provitamin A carotenoids, have been implicated as protecting against certain forms of cancer and cardiovascular disease. ... 

Understanding mechanisms controlling metabolon localization in plastids of different membrane architectures Little is known about metabolon structure, assembly, and membrane targeting. The carotenoid biosynthetic pathway exists on plastid membranes. However, plastids have different membrane architectures and therefore tissue- and plastid-specific differences in membrane targeting of the biosynthetic metabolon can be expected. Localization in chloroplasts that harbor both thylakoid and envelope membranes differs from the envelope membranes in endosperm amy-loplasts. In fact, localization on both thylakoid and envelope membranes implies that the carotenoid pathway is really not a single pathway, but a duplicated pathway that may very well have membrane-specific roles with regard to functions in primary and secondary metabolism. 

Esterbauer et al. (1991) have demonstrated that /3-carotene becomes an effective antioxidant after the depletion of vitamin E. Our studies of LDL isolated from matched rheumatoid serum and synovial fluid demonstrate a depletion of /8-carotene (Section 2.2.2.2). Oncley et al. (1952) stated that the progressive changes in the absorption spectra of LDL were correlated with the autooxidation of constituent fatty acids, the auto-oxidation being the most likely cause of carotenoid degradation. The observation that /3-carotene levels in synovial fluid LDL are lower than those of matched plasma LDL (Section 2.2.2) is interesting in that /3-carotene functions as the most effective antioxidant under conditions of low fOi (Burton and Traber, 1990). As discussed above (Section 2.1.3), the rheumatoid joint is both hypoxic and acidotic. We have also found that the concentration of vitamin E is markedly diminished in synovial fluid from inflamed joints when compared to matched plasma samples (Fairburn etal., 1992). This difference could not be accounted for by the lower concentrations of lipids and lipoproteins within synovial fluid. The low levels of both vitamin E and /3-carotene in rheumatoid synovial fluid are consistent with the consumption of lipid-soluble antioxidants within the arthritic joint due to their role in terminating the process of lipid peroxidation (Fairburn et al., 1992). 

Despite their absence in phycobilisomes, carotenoids, especially the so-called secondary carotenoids such as echinenone, were presumed to play a role in cyanobacterial photoprotection. Indeed, classic biochemical approaches have led to several reports of cyanobacterial carotenoid-proteins and evidence for their photoprotective function (Kerfeld et al. 2003, Kerfeld 2004b). One of these, the water soluble orange carotenoid protein (OCP), has been structurally characterized and has recently emerged as a key player in cyanobacterial photoprotection. 

Absorption and Raman analysis of LHCII complexes from xanthophyll biosynthesis mutants and plants containing unusual carotenoids (e.g., lactucoxanthin and lutein-epoxide) should also be interesting, since the role of these pigments and their binding properties are unknown. Understanding the specificity of binding can help to understand the reasons for xanthophyll variety in photosynthetic antennae and aid in the discovery of yet unknown functions for these molecules. 

Koyama, Y., F. S. Rondonuwu, R. Fujii, and Y. Watanabe. 2004. Light-harvesting function of carotenoids in photosynthesis The roles of the newly found 1B state. Biopolymers 74 2-18. 

Upregulation of retinoid receptor expression and function by provitamin A carotenoids may play a role in mediating the growth inhibitory effects of retinoids in cancer cells (Lian et al. 2006, Prakash et al. 2004). However, it is unclear if non-provitamin A carotenoids and their metabolites may act... 

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