PLANT PHYSIOLOGY , Vol 105, Issue 4 1427-1432, Copyright © 1994 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
Licodione Synthase, a Cytochrome P450 Monooxygenase Catalyzing 2-Hydroxylation of 5-Deoxyflavanone, in Cultured Glycyrrhiza echinata L. Cells
K. Otani, T. Takahashi, T. Furuya and Si. Ayabe
Department of Applied Biological Science, College of Agriculture and Veterinary Medicine, Nihon University, Fujisawa, Kanagawa 252, Japan (K.O., T.T., S.A.)
Cultured Glycyrrhiza echinata L. (Leguminosae) cells produce a
retrochalcone echinatin (4,4[prime]-dihydroxy-2-methoxychalcone) and its
biosynthetic intermediate licodione
[1-(2,4-dihydroxyphenyl)-3-(4-hydroxyphenyl)-1,3-propanedione, a
dibenzoylmethane (keto form) or its enol tautomer
([beta]-hydroxychalcone)], 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
formation of licodione from (2S)-liquiritigenin
(7,4[prime]-dihydroxyflavanone) in the presence of NADPH and air. This
licodione synthase activity was shown to be dependent on cytochrome P450 by
its microsomal localization, requirement of NAD(P)H and O2 for activity,
and inhibition by typical cytochrome P450 inhibitors. Licodione synthase
activity transiently increased in the cells after treatment with yeast
extract. When (2S)-naringenin (5,7,4[prime]-trihydroxyflavanone) and NADPH
were incubated with the same microsomal preparation, a polar compound,
which further converted into apigenin (5,7,4[prime]-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 hemiacetal opening and is possibly the same as the previously
suggested mechanism of flavone synthase II from soybean and, furthermore,
closely related to isoflavone synthase from Pueraria lobata.
