Betalains biosynthesis

Based on genetic studies (cross-breeding) with Portulaca grandma, Trezzini and Zryd (1990) postulated that only three loci are responsible for betalain biosynthesis. While two loci control the bios)mthesis of q/do-Dopa and betalamic acid, the third controls the transport of betalamic acid into the vacuole. They proposed that the formation of betanidin (condensation of cydo-Dopa with betalamic acid) proceeds in the cytoplasm and the formation of betaxan-thins (condensation of betalamic acid with an amino acid/amine) takes place spontaneously in the plant vacuole (Trezzini, 1990). 

Detection of Dopa 4,5-dioxygenase in higher plants and clarification of the level of glucosylation, at betanidin and/or ci/do-Dopa, are the last two steps in betalain biosynthesis to be confirmed. Molecular studies are still needed to elucidate the evolutionary mechanisms of the mutual exclusion of the two pathways (Stafford, 1994), one leading to the ubiquitously occurring anthocyanins and the other to the rare betalains. 

Elliott, D.C. (1983) The pathway of betalain biosynthesis effect of cytokinin on enzymic oxidation and hydroxylation of tyrosine in Amaranthus tricolor seedlings. 

Mueller, L.A., Hinz, U. and Zryd, J.-P. (1996) Characterization of a tyrosinase from Amanita muscaria involved in betalain biosynthesis. Phytochemistry, 42,1511-5. 

Steiner, U., Schliemarm, W., Bohm, H. and Strack, D. (1999) Tyrosinase involved in betalain biosynthesis of higher plants. Planta, 208,114—24. 

It should be emphasized here that there is a general lack of knowledge on the enzymology of betalain formation. This contrasts with the considerable progress that has been made in work on the biosynthesis of the analogous water-soluble flavonoids (99). The possible reactions involved in betalain biosynthesis have been deduced from feeding experiments with isotopically labeled dopa and tyrosine (115-119), which support the early suggestion of Wyler et al. (5) that dopa is the ultimate precursor for both the betalamic acid moiety in betaxanthins and betacyanins as well as the cyclodopa part in betacyanins. Furthermore,... 

Further evidence implicating betalamic acid (176) in betalain biosynthesis comes from a study of the biosynthesis of the acid itself in Portulaca grandifiora Both [2- CJ- and [l- C]-DL-dopa were incorporated into betalamic acid. Degradation of the betalamic acid (176) derived from [l- C]dopa showed that the incorporation was specific, almost all the activity being confined to the carboxy-groups (and presumably only C-19 is labelled). This pattern of dopa incorporation is the same as for the betalains, a requirement if (176) is to be an intermediate in betalain biosynthesis. 

Anthramycin.—The aromatic ring of tyrosine suffers minor modification on incorporation into securinine (see above) whilst utilization in betalain biosynthesis results in ring cleavage between C-3 and C-4 after hydroxylation to dopa (see below). Similar degradation of tyrosine occurs in the biosynthesis of anthramycin (166), an antibiotic produced by Streptomyces refuineus. var thermotolerans. ... 

This is in accord with a mechanism involving hydroxylation of tyrosine to give dopa (with expected loss of half the tritium), meta cleavage (which is formally similar to the mechanism of cleavage in betalain biosynthesis), and finally loss of two ring carbons (see Scheme 17, where the alternative ortho cleavage is also... 

Cetosia plumosa was selected for further studyof betalain biosynthesis as yellow varieties of this species showed, on administration of appropriate substrates, an ability to synthesize the red pigment amaranthin (189) normally produced by other varieties of the same species. The experimental work was thus simplified because in some cases it was not necessary to employ radioactive precursors the consequence of feeding a particular substrate could be correlated with the appearance of red pigment. 

Physiological Activity of Xanthine Derivatives Pyrazine Alkaloids Securinega Alkaloids Sesbania Alkaloids Betalains Biosynthesis Chemosystematic Value Betalains in Foods and Beverages Miscellaneous Alkaloids Trigonelline and an Unusual Pyrrole Histronionicotoxins Huperzine A References... 

Betalain biosynthesis starts with dopa by opening of its benzene ring, followed by cyclization to a dihydropyridine. The (S)-betalamic acid which is formed undergoes condensation with (S)-cyclodopa to betacyanins or with some other amino acids to betaxanthins (cf. reaction sequence 17.21). 

Delgado-Vargas, R, Jimenez, A.R., and Paredes-Lopez O., Natural pigments carotenoids, anthocyanins, and betalains — characteristics, biosynthesis, processing, and stability, Crit. Rev. Food Sci. Nutr., 40, 173, 2000. 

Schliemaim, W. et al., Betalains of Celosia argentea. Phytochemistry, 58, 159, 2001. Schliemaim, W., Kobayashi, N., and Stack, D., The decisive step in betaxanthin biosynthesis is a spontaneous reaction. Plant Physiol., 119, 1217, 1999. 

One of the most important applications of PPO, although rarely reported, is its role in synthetic processes, such as the biosynthesis of betalains. Several researchers reported the hydroxylation of tyrosine to dopa, which can then be oxidized to dopaquinone, through a PPO from Portulaca grandiflora and from Beta vulgaris. Thus, a dioxygenase activity complements the constitutive PPO activity and the initiation of this dioxygenase... 

Keywords alkaloid biosynthesis alkaloid genes nicotine tropane alkaloids pyrrolizidine alkaloids benzylisoquinoline alkaloids monoterpene indole alkaloids ergot alkaloids acridone alkaloids purine alkaloids taxol betalains... 

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