Formation of 6'-Deoxychalcone 4'-Glucosides by Enzyme Extracts from Petals of Dahlia variabilis

Abstract

Yellow colouration of Dahlia variabilis is mainly provided by isoliquiritigenin 4′-glucoside and butein 4′-glucoside. Incubation of petal extracts with uridin 5′-diphosphoglucose and isoliquiritigenin or butein led to the formation of one product which was identified as the respective 6′-deoxychalcone 4′-glucoside. Glucosylation of hydroxyl groups in other positions was not observed. Naringenin chalcone and eriodictyol chalcone were not accepted as substrates. The 4′-glucosylation of isoliquiritigenin and butein showed a broad pH optimum ranging from pH 7 to 8 and was stimulated by Mg2+, Ca2+ and Mn2+. N-Ethylmaleimide, p-hydroxymercuribenzoate, Cu2+, Zn2+, and Fe2+ clearly reduced the activity of the enzyme. The apparent Km values for UDP-glucose, isoliquiritigenin and butein were 90, 26 and 276 [μᴍ respectively.