This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Biosynthesis → Secondary Metabolites Biosynthesis|
indican is the β-D-glucoside of indoxyl, and is found in several plant families, the most important being Acanthaceae, Asclepiadaceae, Apocynaceae, Fabaceae, and Polygonaceae. The function of indican in plants is still unknown.
After enzymic or chemical hydrolysis, indican can converted back to indoxyl, which can spontaneously dimerize (in the presence of oxygen) to indigo. Indigo was one of the most important dye compounds in the past, and is still an esteemed dye today.
The pathway for indican biosynthesis diverts from that of L-tryptophan at indole, which is produced from (1S,2R)-1-C-(indol-3-yl)glycerol 3-phosphate by the tryptophan synthase subunit α. Indole is converted by dioxygenase systems (enzyme complexes that form cis-dihydrodiols) to cis-indole-2,3-dihydrodiol, which spontaneously eliminate a water molecule to form indoxyl. While dioxygenase enzymes from the plants that are konwn to produce indigo have not been studied yet, bacterial enzymes, such as naphthalene 1,2-dioxygenase from Pseudomonas putida, have been used successfully for the production of indican in strain of Escherichia coli engineered to produce indigo [Ensley83a].
In the plant, indoxyl is converted to indican by indoxyl-UDPG glucosyltransferase. This enzyme has been purified from Baphicacanthus cusia [Marcinek00] and Persicaria tinctoria [Minami00]. However, as mentioned above, in the absence of this enzyme indoxyl can dimerize spontaneously to indigo.
Ensley83a: Ensley BD, Ratzkin BJ, Osslund TD, Simon MJ, Wackett LP, Gibson DT (1983). "Expression of naphthalene oxidation genes in Escherichia coli results in the biosynthesis of indigo." Science 222(4620);167-9. PMID: 6353574
Minami00: Minami Y, Nishimura O, Hara-Nishimura I, Nishimura M, Matsubara H (2000). "Tissue and intracellular localization of indican and the purification and characterization of indican synthase from indigo plants." Plant Cell Physiol 41(2);218-25. PMID: 10795317
Haigler90a: Haigler BE, Gibson DT (1990). "Purification and properties of ferredoxinNAP, a component of naphthalene dioxygenase from Pseudomonas sp. strain NCIB 9816." J Bacteriol 172(1);465-8. PMID: 2294093
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