Carotenoid function

Many carotenoids function in humans as vitamin A precursors however, not all carotenoids have provitamin A activity (Table 3). Of the biologically active carotenoids, -carotene has the greatest activity. Despite the fact that theoretically one molecule of -carotene is a biological source of two molecules of vitamin A, this relationship is not observed and 6 p.g -carotene is equivalent to 1 p. vitamin A. Although -carotene and vitamin A have complementary activities, they caimot totally replace each other. Because the conversion of -carotene to vitamin A is highly regulated, toxic quantities of vitamin A cannot accumulate and -carotene can be considered as a safe form of vitamin A (8). 

Bertram, J. S. 2004. Induction of connexin 43 by carotenoids Functional consequences. Arch Biochem Biophys 430(1) 120-126. 

Carotenoids function along with chlorophylls in photosynthesis as accessory light-harvesting... 

Cogdell, R. J., and Frank, H. A., 1987, How carotenoids function in photosynthetic bacteria. Biochim. Biophys. Acta, 895 63n79. 

Springer Sot Chem Phys 42 62-66 Cogdell RJ and Frank HA (1987) How Carotenoids function in photosynthetic bacteria. Biochim Biophys Acta 895 63-79 Condon EU (1926) A theory of intensity distribution in band systems. Phys Rev 28 1182-1201 Condon EU (1947) The Franck-Condon Principle and Related Topics. Am J Phys 15 365-374 Crofts AR and Yerkes CT (1994) A molecular mechanism for quenching. FEES Lett 352 265-270 de Grooth BG, van Grondelle R, Romijn JC and Pulles MPJ (1979) The mechanism of reduction of the ubiquinone pool in photosynthetic bacteria at different redox potential. Biochim Biophys Acta 503 480-490... 

Carotenoids function in photosynthesis as quenchers of chlorophyll triplet states to prevent their harmful reaction with oxygen. Current research has mainly focused on their detection and identification, the determination of kinetic parameters, and the elucidation of the triplet energy transfer pathways in both photosynthetic antenna and reaction centers. Since carotenoids do not take part in the photosynthetic electron transfer reactions, their paramagnetic radical species occur to a lesser extent in vivo, although they may play arole in the photoprotection of Photosystem II. 

Carotenoids function in photosynthetic reaction centers (RC) as triplet quenchers of the primary donor chlorophyll or bacteriochlorophyll triplet states. The best studied RCs are those of purple photosynthetic bacteria where atomic models are available based on X-ray crystallography and optical as well as magnetic resonance spectroscopies have yielded a detailed picture of the flow of triplet energy transfer. Good reviews of these topics can be found in (Frank, 1992, 1993 Frank and Cogdell, 1996). 

Foote CS, Chang YC and Deeny RW (1970) Chemistry of singlet oxygen. X. Carotenoid quenching parallels biological protection. J Am Chem Soc 92 5216-5218 Frank HA and Cogdell RJ (1987) How carotenoids function in... 

Mordi, R.C. Carotenoids-function and degradation. Chemistry and Industry, 110, 79-83. 1993. 

---