SINGLET OXYGEN AND PEROXYL RADICALS REGULATE CAROTENOID BIOSYNTHESIS IN PHAFFIA-RHODOZYMA

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-1(2)) and peroxyl radicals differently affect carotenoid composition and biosynthesis in the yeast Phaffia rhodozyma. Photochemical generation of (1)0(2) with rose bengal or alpha-terthienyl induced carotenoid accumulation. In contrast, peroxyl radicals derived from t-butylhydroperoxide (tBOOH) or H2O2 decreased the content of astaxanthin and increased beta-carotene by similar to 4-fold, suggesting end product feedback regulation by astaxanthin or inhibition of bio synthetic enzymes, C-14 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 C40H52O3. Chemical derivatizations combined with mass and absorbance spectroscopy tentatively identified the carotenoid as dehydroflexixanthin (3,1'-dihydroxy2,3,3 ',4'-tetradehydro 1',2'-dihydro beta,psi-carotene-4-one). This study provides the first report of induction of astaxanthin biosynthesis by (1)0(2), probable feedback control by astaxanthin, and the oxidative degradation of astaxanthin to novel pigments in P. rhodozyma.