CAROTENOIDS AS SINGLET OXYGEN QUENCHERS IN MARINE ORGANISMS

To understand the roles of carotenoids as singlet oxygen quenchers in marine organisms, quenching activities of eight major carotenoids, ast axanthin, canthaxanthin, beta-carotene, zeaxanthin, lutein, tunaxanthi n, fucoxanthin and halocynthiaxanthin were examined according to the m ethod using a thermodissociable endoperoxide of 1,4-dimethylnaphthalen e as a singlet oxygen generator. The second-order rate constant for th e singlet oxygen quenching activity by each carotenoid was determined, suggesting that an increasing number of conjugated double bonds in ca rotenoid was proportional to greater quenching activity. The quenching activity of each carotenoid was found to be approximately 40 to 600 t imes greater than that of alpha-tocopherol. The potency of these carot enoids suggests that they may play a role in protecting marine organis ms from active oxygen species.