Carotenoid photooxidation in photosystem II

Carotenoids are known to function as light-harvesting pigments and they pla y important roles in photoprotection in both plant rind bacterial photosynt hesis. These functions are also important for carotenoids in photosystem II . In addition, beta -carotene recently has been found to function as a redo x intermediate in an alternate pathway of electron transfer within photosys tem II. This redox role of a carotenoid in photosystem II is unique among p hotosynthetic reaction centers and stems from the very highly oxidizing int ermediates that form in the process of water oxidation. In this minireview, an overview of the electron-transfer reactions in photosystem II is presen ted, with an emphasis on those involving carotenoids, The carotenoid compos ition of photosystem II and the physical methods used to study the structur e of the redox-active carotenoid are reviewed. Possible roles of carotenoid cations in photoprotection of photosystem II are discussed, (C) 2001 Acade mic Press.