STRUCTURE AND PROPERTIES OF CAROTENOIDS IN RELATION TO FUNCTION

The basic principles of structure, stereochemistry, and nomenclature o f carotenoids are described and the relationships between structure an d the chemical and physical properties on which all the varied biologi cal functions and actions of carotenoids depend are discussed. The con jugated polyene chromophore determines not only the light absorption p roperties, and hence color, but also the photochemical properties of t he molecule and consequent light-harvesting and photoprotective action . The polyene chain is also the feature mainly responsible for the che mical reactivity of carotenoids toward oxidizing agents and free radic als, and hence for any antioxidant role. In vivo, carotenoids are foun d in precise locations and orientations in subcellular structures, and their chemical and physical properties are strongly influenced by oth er molecules in their vicinity, especially proteins and membrane lipid s. In turn, the carotenoids influence the properties of these subcellu lar structures. Structural features such as size, shape, and polarity are essential determinants of the ability of a carotenoid to fit corre ctly into its molecular environment to allow it to function. A role fo r carotenoids in modifying structure, properties, and stability of cel l membranes, and thus affecting molecular processes associated with th ese membranes, may be an important aspect of their possible beneficial effects on human health.