Interaction of chlorophyll a with β-carotene in phosphatidyl choline bilayers

Abstract

Carotenoids constitute an essential part of the photochemical reaction systems of photosynthesis. Although carotenes are able to quench the triplet state of chlorophyll in organic solutions and lipid micelles, their function in the transfer of energy in photosynthesis is not clear. As an in vitro model for these processes, a study was undertaken of the fluorescence of chlorophyll a in phosphatidyl choline vesicles prepared with and without β-carotene. The quenched fluorescence of chlorophyll, observed in the mixed bilayers, is interpreted as the result of complex formation with the carotene. A mechanism proposed for this effect is an interaction between the two pigment species which would give rise to special chlorophyll a pairs upon trans-cis photoisomerizations of the β-carotene polyenic chain. It is suggested that such mechanisms may prevent the formation of wasteful quenching centers by limiting to about 14 Å the nearest-neighbor distance between chlorophyll a molecules.