Hydroxylation of the B-Ring of Flavonoids in the 3′-and 5′-Position with Enzyme Extracts from Flowers of Verbena hybrida

Enzyme preparations from flowers of Verbena hybrida do not only catalyse hydroxylation of the B-ring of flavanones and dihydroflavonols in the 3′-position but also in the 5′-position. Enzyme activity for 3′,5′-hydroxylation was found to be localized in the microsomal fraction and required NAD PH as cofactor. Evidence is provided that the formation of the 3′,4′,5′-hydroxylated flavanone (5,7,3′,4′,5′-pentahydroxyflavanone) and dihydroflavonol (dihydromyricetin), respectively, proceeds via the corresponding 3′,4′-hydroxylated compounds eriodictyol and dihydroquercetin, respectively, which are most probably formed by action of the same enzyme. Enzyme activity for 3′,5′-hydroxylation was found to be strictly correlated with the prescence of 3′,4′,5′-hydroxylated flavonoid compounds in the flowers.