Carotenoids have recently received considerable interest because of their potential in delaying or preventing degenerative diseases such as arteriosclerosis, cancer, and aging. In this study we show that the active oxygen species singlet oxygen (O) and peroxyl radicals differently affect carotenoid composition and biosynthesis in the yeast Phaffia rhodozyma. Photochemical generation of O with rose bengal or -terthienyl induced carotenoid accumulation. In contrast, peroxyl radicals derived from t-butylhydroperoxide (tBOOH) or HO decreased the content of astaxanthin and increased -carotene by 4-fold, suggesting end product feedback regulation by astaxanthin or inhibition of biosynthetic enzymes. C labeling of carotenoids during oxidative stress supported the possibility of end product regulation. Carotenoids were bleached by 8 mM tBOOH within 6 h when carotenogenesis was inhibited by thymol. When treated with peroxides, a previously unreported pigment in P. rhodozyma was formed. The carotenoid had a mass of 580 Da and a molecular formula of CHO. Chemical derivatizations combined with mass and absorbance spectroscopy tentatively identified the carotenoid as dehydroflexixanthin (3,1`-dihydroxy-2,3,3`,4`-tetradehydro-1`,2`-dihydro-,-carotene-4-one). This study provides the first report of induction of astaxanthin biosynthesis by O, probable feedback control by astaxanthin, and the oxidative degradation of astaxanthin to novel pigments in P. rhodozyma.

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