Enzymatic hydroxylation of 6'-deoxychalcones with protein preparations from petals of Dahlia variabilis

Yellow colouration of Dahlia variabilis flowers is mainly based on isoliquiritigenin and butein 4'-malonylglucosides. Microsomal preparations from petals of the yellow strain 'Johann Nestroy' catalyse the enzymatic 3- hydroxylation of isoliquiritigenin to butein in the presence of NADPH. The reaction showed a pH optimum of 7.5, and was inhibited by p- hydroxymercuribenzoate and a number of cytochrome P450 specific inhibitors. These and further properties suggest that the 3-hydroxylation of isoliquiritigenin is mediated by a cytochrome P450-dependent monooxygenase. The apparent K(m) value for isoliquiritigenin was 50 μM.