title: The biosynthesis of cyclic carotenes.
abstract: 1. The incorporation of (3RS)-[2-(14)C,(4R)-4-(3)H(1)]mevalonic acid into various cyclic carotenes in the fruit of the tomato mutant delta has been studied. The results confirm our previous view that the alpha-ionone ring of alpha-carotene does not arise by isomerization of a beta-ionone residue, and show that the same is also true for the alpha-ionone ring of delta- and in-carotene and alpha-zeacarotene. 2. The incorporation of (3RS)-[2-(14)C,2-(3)H(2)]mevalonic acid into alpha- and beta-carotene in carrot roots has been studied. The results show that the beta-ionone ring of beta-carotene does not arise by isomerization of the alpha-ionone residue of alpha-carotene. 3. These experiments show that alpha- and beta-ionone rings in cyclic carotenes are formed independently, probably by elimination of different protons from the same carbonium ion intermediates.
mesh_terms: D002247:Carbon Isotopes; D002338:Carotenoids / Q000096:biosynthesis* / Q000378:metabolism; D008798:Mevalonic Acid / Q000378:metabolism*; D008954:Models, Biological; D008956:Models, Chemical; D009154:Mutation; D010945:Plants, Edible / Q000378:metabolism*; D011522:Protons; D014316:Tritium
chemical_list: D002247:Carbon Isotopes; D011522:Protons; D014316:Tritium; D002338:Carotenoids; D008798:Mevalonic Acid