UDP-glucose + a flavonol UDP + a flavonol 3-O-beta-D-glucoside
The two substrates of this enzyme are UDP-glucose and a flavonol. Its products are uridine diphosphate (UDP) and the corresponding flavonol 3-O-beta-D-glucoside. The flavonoids that can act as substrates within this reaction include quercetin, kaempferol, dihydrokaempferol, kaempferid, fisetin, and isorhamnetin. Flavonol 3-O-glucosyltransferase is a hexosyl group transfer enzyme.[1]
This enzyme is known by the systematic name UPD-glucose:flavonol 3-O-D glucosyltransferase, and it participates in flavonoid biosynthesis and causes the formation of anthocyanins. Anthocyanins produce a purple color in the plant tissues that they are present in.[2]
This enzyme is involved in the biosynthesis of secondary metabolites. The primary function of this enzyme within its pathway is binding a glucoside onto a flavonol molecule, forming a flavonol 3-O-glucoside. For example, it converts quercetin to isoquercetin:[1]
A glucose unit is transferred from UDP-glucose to a specific hydroxy group of the flavonol, with uridine diphosphate (UDP) as a byproduct. By the same mechanism, the enzyme converts anthocyanidins to anthocyanins as a part of the phenylpropanoid pathway. For example, pelargonidin is transformed into callistephin (pelargonidin 3-O-glucoside).
This enzyme is also involved in the flavone glycoside pathway, and daphnetin modification in some organisms.[8]
Nomenclature
This enzyme belongs to the family of glycosyltransferases, specifically the hexosyltransferases. The systematic name of this enzyme class is UDP-glucose:flavonol 3-O-D-glucosyltransferase. Other names in common use include:
Among those, UFGT is divided into UDP-glucose: Flavonoid 3-O-glucosyltransferase (UF3GT) and UDP-glucose: Flavonoid 5-O-glucosyltransferase (UF5GT), which are responsible for the glucosylation of anthocyanins to produce stable molecules.[6]
Inhibitors and Structure of the Enzyme
Some of the inhibitors of this enzyme include CaCl2, CoCl2, Cu+2, CuCl2, KCl, Mg+2, and Mn+2.[9] The primary active site residue of this enzyme is Asp181, as determined by studies of how mutations affect enzyme capacity.[10] There are several documentations of the crystalline structure of flavonol 3-O-glucosyltransferase (2C1X, 2C1Z, and 2C9Z),[11] and, based on these renderings of the enzyme, there is only one subunit in the quaternary structure of the molecule.
References
↑ 1.01.1Kleinehollenhorst, G.; Behrens, H.; Pegels, G.; Srunk, N.; Wiermann, R. (1982). "Formation of Flavonol 3-O-Diglycosides and Flavonol 3-O-Triglycosides by Enzyme Extracts from Anthers of Tulipa cv. Apeldoorn / Characterization and Activity of Three Different O -Glycosyltransferases during Anther Development". Zeitschrift für Naturforschung C37 (7–8): 587–599. doi:10.1515/znc-1982-7-808.
↑Dooner, H. K.; Nelson, O. E. (1977). "Genetic control of UDPglucose:flavonol 3-O-glucosyltransferase in the endosperm of maize". Biochemical Genetics15 (5–6): 509–519. doi:10.1007/BF00520194. PMID880210.
↑"UDP-glucose: flavonol 3-0-glucosyltransferase from cell suspension cultures of parsley". Biochim. Biophys. Acta309 (2): 289–95. 1973. doi:10.1016/0005-2744(73)90027-2. PMID4731963.
↑Wiermann R (1982). "Formation of flavonol 3-O-diglycosides and flavonol 3-O-triglycosides by enzyme extracts from anthers of Tulipa cv apeldoorn - characterization and activity of 3 different O-glycosyltransferases during anther development". Z. Naturforsch. C37: 587–599. doi:10.1515/znc-1982-7-808.
↑ 6.06.1"Isolation of a UDP-glucose: Flavonoid 5-O-glucosyltransferase gene and expression analysis of anthocyanin biosynthetic genes in herbaceous peony (Paeonia lactiflora Pall.)". Electronic Journal of Biotechnology15 (6). November 2012. doi:10.2225/vol15-issue6-fulltext-7.