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.
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.
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:
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.
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.
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. The primary active site residue of this enzyme is Asp181, as determined by studies of how mutations affect enzyme capacity. There are several documentations of the crystalline structure of flavonol 3-O-glucosyltransferase (2C1X, 2C1Z, and 2C9Z), and, based on these renderings of the enzyme, there is only one subunit in the quaternary structure of the molecule.
↑Dooner, H. K.; Nelson, O. E. (1977). "Genetic control of UDPglucose:flavonol 3-O-glucosyltransferase in the endosperm of maize". Biochemical Genetics. 15 (5–6): 509–519. doi:10.1007/BF00520194. PMID880210.
↑Kobayashi S, Ishimaru M, Ding CK, Yakushiji H, Goto N (February 2001). "Comparison of UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGT) gene sequences between white grapes (Vitis vinifera) and their sports with red skin". Plant Sci. 160 (3): 543–550. Bibcode:2001PlnSc.160..543K. doi:10.1016/S0168-9452(00)00425-8. PMID11166442.
↑Sutter A, Grisebach H (1973). "UDP-glucose: flavonol 3-0-glucosyltransferase from cell suspension cultures of parsley". Biochim. Biophys. Acta. 309 (2): 289–95. doi:10.1016/0005-2744(73)90027-2. PMID4731963.
↑Schomburg, Professor Dietmar; Schomburg, Dr Ida, eds. (1 January 2006). "Flavonol 3-O-glucosyltransferase". Springer Handbook of Enzymes. Vol.32. Springer Berlin Heidelberg. pp.21–29. doi:10.1007/978-3-540-49534-5_2. ISBN978-3-540-32591-8.
