In enzymology, a flavonol 3-O-glucosyltransferase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are UDP-glucose and flavonol, whereas its two products are UDP and 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.
It is an enzyme found most notably in grapes (Vitis vinifera). This enzyme is found within a number of other plants as wellâÂÂsuch as snapdragons (Antirrhinum majus), kale (Brassica oleracea), and grapefruit (Citrus x paradisi).
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. It is through this mechanism that the enzyme converts anthocyanidins to anthocyanins as a part of the phenylpropanoid pathway. One specific example would be this enzymes actions on pelargonidin. Flavonol 3-O-glucosyltransferase binds the glucoside to this protein, making pelargonidin 3-O-glucoside. This enzyme is also involved in the flavone glycoside pathway, and daphnetin modification in some organisms. The role of the enzyme in these pathways is, again, to bind a glucoside to the substrate to construct a flavonol 3-O-glucoside.
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.
Some of the inhibitors of this enzyme include CaCl<sub>2</sub>, CoCl<sub>2</sub>, Cu<sup>+2</sup>, CuCl<sub>2</sub>, KCl, Mg<sup>+2</sup>, and Mn<sup>+2</sup>. 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.