Biosynthesis of Vitexin and Isovitexin: Enzymatic Synthesis of the C-Glucosylflavones Vitexin and Isovitexin with an Enzyme Preparation from Fagopyrum esculentum M. Seedlings

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Abstract
A C-glucosyltransferase from Fagopyrum esculentum seedlings catalyzes the transfer of glucose from UDP-glucose or ADP-glucose to 2-hydroxyflavanones. In cell-free enzyme preparations it was shown that only 2-hydroxyflavanones, e.g. 2,4′,5,7-tetrahydroxyflavanone and 2,5,7-trihydroxyflavanone were appropriate substrates. Naringenin, naringenin-chalcone and the flavones apigenin and chrysin cannot act as glucosyl acceptors in C-glucosyl-flavonoid biosynthesis. This demonstrates that C-glucosylation occurs after oxidation of flavanones.