Springer Online Journal Archives 1860-2000
Abstract Green plants use the xanthophyll cycle to regulate the flow of energy to chlorophylla within photosynthetic proteins. Under conditions of low light intensity violaxanthin, a carotenoid possessing nine conjugated double bonds, functions as an antenna pigment by transferring energy from its lowest excited singlet state to that of chlorophylla within light-harvesting proteins. When the light intensity increases, violaxanthin is biochemically transformed into zeaxanthin, a carotenoid that possesses eleven conjugated double bonds. The results presented here show that extension of the ⧄ conjugation of the polyene lowers the energy of the lowest excited singlet state of the carotenoid below that of chlorophylla. As a consequence zeaxanthin can act as a trap for the excess excitation energy on chlorophylla pigments within the protein, thus regulating the flow of energy within photosynthetic light-harvesting proteins.
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