diadinoxanthin and neoxanthin

Carotenoids are essential components of photosynthetic organisms including land plants, algae, cyanobacteria, and photosynthetic bacteria. Although the light-mediated regulation of carotenoid biosynthesis, including the light/dark cycle as well as the dependence of carotenoid biosynthesis-related gene translation on light wavelength, has been investigated in land plants, these aspects have not been studied in microalgae. Here, we investigated carotenoid biosynthesis in Euglena gracilis and found that zeaxanthin accumulates in the dark. The major carotenoid species in E. gracilis, namely β-carotene, neoxanthin, diadinoxanthin and diatoxanthin, accumulated corresponding to the duration of light irradiation under the light/dark cycle, although the translation of carotenoid biosynthesis genes hardly changed. Irradiation with either blue or red-light (3 μmol photons m

Topics: Acclimatization; beta Carotene; Chlorophyll; Euglena gracilis; Gene Expression Regulation; Light; Photosystem II Protein Complex; Xanthophylls; Zeaxanthins

The biosynthesis pathway to diadinoxanthin and fucoxanthin was elucidated in Phaeodactylum tricornutum by a combined approach involving metabolite analysis identification of gene function. For the initial steps leading to β-carotene, putative genes were selected from the genomic database and the function of several of them identified by genetic pathway complementation in Escherichia coli. They included genes encoding a phytoene synthase, a phytoene desaturase, a ζ-carotene desaturase, and a lycopene β-cyclase. Intermediates of the pathway beyond β-carotene, present in trace amounts, were separated by TLC and identified as violaxanthin and neoxanthin in the enriched fraction. Neoxanthin is a branching point for the synthesis of both diadinoxanthin and fucoxanthin and the mechanisms for their formation were proposed. A single isomerization of one of the allenic double bounds in neoxanthin yields diadinoxanhin. Two reactions, hydroxylation at C8 in combination with a keto-enol tautomerization and acetylation of the 3'-HO group results in the formation of fucoxanthin.

Topics: beta Carotene; Biosynthetic Pathways; Carotenoids; Diatoms; Escherichia coli; Genetic Complementation Test; Geranylgeranyl-Diphosphate Geranylgeranyltransferase; Intramolecular Lyases; Oxidoreductases; Phylogeny; Xanthophylls; zeta Carotene

Intact cells of the alga Amphidinium carterae (Dinophyceae), and a cell-free system prepared from it, incorporated 14C, 3H-labelled mevalonate into lycopene, beta, beta-carotene, zeaxanthin, neoxanthin, diadinoxanthin and peridinin. The 14C/3H ratios of zeaxanthin, neoxanthin and diadinoxanthin formed from (2RS,3R)-[2-14C,2-3H2]mevalonate show that a hydrogen atom from C-2 of mevalonate is retained in the allene at C-8, and also at C-12 of peridinin. (3R,4R + 3S,4S)-[2-14C,4-3H1]Mevalonate gave 14C/3H ratios in peridinin which show that C-14 is lost. The three carbon atoms excised during the formation of the C37 carotenoid peridinin are C-13, C-14 and C-20 of neoxanthin.

Topics: Acetylene; Carotenoids; Cell-Free System; Chemical Phenomena; Chemistry; Eukaryota; Mevalonic Acid; Molecular Conformation; Xanthophylls