ALTERNATIVE PATHWAYS OF XANTHONE BIOSYNTHESIS IN CELL-CULTURES OF HYPERICUM-ANDROSAEMUM L

The biosynthesis of xanthones was studied in cell cultures of Hypericu m androsaemum L. We have detected a new benzophenone synthase, for whi ch the preferred substrate is benzoyl-CoA, itself supplied by 3-hydrox ybenzoate:coenzyme A ligase. The stepwise condensation of benzoy1-CoA with three molecules of malonyl-CoA, catalyzed by benzophenone synthas e, yields 2,4,6-trihydroxybenzophenone. This intermediate is subsequen tly converted by benzophenone 3'-hydroxylase, a cytochrome P450 monoox ygenase, These biosynthetic steps, leading to the formation of 2,3',4, 6-tetrahydroxybenzophenone, represent an alternative pathway to that r ecently proposed for cell cultures of Centaurium erythraea [Peters et al., Planta (1997) in press]. (C) 1997 Federation of European Biochemi cal Societies.