Alternative pathways of xanthone biosynthesis in cell cultures of Hypericum androsaemum L

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Abstract
The biosynthesis of xanthones was studied in cell cultures of Hypericum androsaemum L. We have detected a new benzophenone synthase, for which the preferred substrate is benzoyl-CoA, itself supplied by 3-hydroxybenzoate:coenzyme A ligase. The stepwise condensation of benzoyl-CoA with three molecules of malonyl-CoA, catalyzed by benzophenone synthase, yields 2,4,6-trihydroxybenzophenone. This intermediate is subsequently converted by benzophenone 3′-hydroxylase, a cytochrome P450 monooxygenase. These biosynthetic steps, leading to the formation of 2,3′,4,6-tetrahydroxybenzophenone, represent an alternative pathway to that recently proposed for cell cultures of Centaurium erythraea [Peters et al., Planta (1997) in press]