LICODIONE SYNTHASE, A CYTOCHROME-P450 MONOOXYGENASE CATALYZING 2-HYDROXYLATION OF 5-DEOXYFLAVANONE, IN CULTURED GLYCYRRHIZA-ECHINATA L CELLS

Cultured Glycyrrhiza echinata L. (Leguminosae) cells produce a retroch alcone echinatin (4,4'-dihydroxy-2-methoxychalcone) and its biosynthet ic intermediate licodione droxyphenyl)-3-(4-hydroxyphenyl)-1,3-propane dione, a dibenzoylmethane (keto form) or its enol tautomer (beta-hydro xychalcone)], when treated with elicitor-active substances, e.g. yeast extract. A microsomal fraction (160,000g pellet) prepared from yeast extract-induced suspension cultures of G. echinata catalyzed the forma tion of licodione from (2S)-liquiritigenin (7,4'-dihydroxyflavanone) i n the presence of NADPH and air. This licodione synthase activity was shown to be dependent on cytochrome P450 by its microsomal localizatio n, requirement of NAD(P)H and O-2 for activity, and inhibition by typi cal cytochrome P450 inhibitors. Licodione synthase activity transientl y increased in the cells after treatment with yeast extract. When (2S) -naringenin (5,7,4'-trihydroxyflavanone) and NADPH were incubated with the same microsomal preparation, a polar compound, which further conv erted into apigenin (5,7,4'-trihydroxyflavone) when treated with acid, was produced. The reaction mechanism of licodione synthase is likely to be 2-hydroxylation of the flavanone molecule and subsequent hemiace tal opening and is possibly the same as the previously suggested mecha nism of flavone synthase II from soybean and, furthermore, closely rel ated to isoflavone synthase from Pueraria lobata.