The Biosynthesis of Carotenes in the Tomato

Citation

Thompson, Guy Allen (1959) The Biosynthesis of Carotenes in the Tomato. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/SXP9-4527. https://resolver.caltech.edu/CaltechETD:etd-02232006-084220

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Ripening tomatoes were injected with 1C(14)-acetic acid or 2C(14)-mevalonic(3,5-dihydroxy-3-methylvaleric) acid and, after various incubation times, the carotenes were extracted and purified. The pattern of labeling among the carotenes leads to the conclusion that the more unsaturated pigments are not formed by the dehydrogenation of less unsaturated carotenes, but, rather, that most carotenes are synthesized by independent pathways, although from common precursors. 2C(14)-Mevalonic acid was found to be incorporated into the carotene fraction with high efficiency. Most of the radioactivity was found by chromatographic separation of the polyenes to be associated with the phytoene fraction. Purification of this fraction yielded phytoene of little radioactivity and an unknown compound of specific activity higher than that of any purified carotene. This compound, designated as fraction II, has been shown to be a 20-carbon-atom isoprenoid hydrocarbon containing a pair of conjugated double bonds. Its probable structure is given below. [...] Fraction II is rapidly synthesized from mevalonic acid in both ripening and immature tomatoes. A complete pathway for the formation of the carotenes from mevalonic acid is proposed. It is postulated that fraction II is formed throuhghout the life of the fruit and is continuously converted to an as yet uncharacterized polyene, which yields carotenes at the time of ripening. The incorporation into carotenes of C(14)O(2), 1C(14)-glucose, uniformly C(14)-labeled-glucose, and uniformly C(14)-labeled leucine is described, and the patterns of labeling are compared with those obtained using mevalonate or acetate.

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