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 NADPH as cofactor. Evidence is provided that the formation of the 3',4',5'- hydroxylated flavanone (5,7,3',4',5'-pentahydroxyflavanone) and dihydroflavonol (dihydromy- ricetin), 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.