Formation of 6'-deoxychalcone 4'-glucosides by enzyme extracts from petals of Dahlia variabilis

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 Kmvalues for UDP-glucose, isoliquiritigenin and butein were 90, 26 and 276 µM respectively.