UDP-glucose + a flavonol UDP + a flavonol 3-O-beta-D-glucoside
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.[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.[5] 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.[6]
The structure of pelargonidin.The structure of pelargonidin 3-O-glucoside.
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.[7]
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.[8] The primary active site residue of this enzyme is Asp181, as determined by studies of how mutations affect enzyme capacity.[9] There are several documentations of the crystalline structure of flavonol 3-O-glucosyltransferase (2C1X, 2C1Z, and 2C9Z),[10] and, based on these renderings of the enzyme, there is only one subunit in the quaternary structure of the molecule.
^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. doi:10.1016/S0168-9452(00)00425-8. PMID11166442.
^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.
