STYRYLPYRONE BIOSYNTHESIS IN EQUISETUM-ARVENSE

Styrylpyrone synthase was detected in cell free extracts from gametoph ytes of Equisetum arvense. This new enzyme catalyses the formation of styrylpyrones from malonyl-CoA and hydroxycinnamoyl-CoA precursors. A standard enzyme assay was established. The enzyme activity was charact erized in partially purified protein extracts. p-Coumaroyl-CoA was acc epted as substrate at pH 6.0-8.5 in various buffer systems with the fo rmation of bisnoryangonin, and optimum enzyme activity was observed in potassium phosphate buffer at pH 7.5. Caffeoyl-CoA was accepted as su bstrate only in potassium phosphate buffer at pH 6.0-7.5 with formatio n of hispidin; optimum enzyme activity was observed at pH 7.0. The app arent K-m values were 220 mu M for caffeoyl-CoA and 230 mu M for p-cou maroyl-CoA. The temperature optimum of the enzyme activity was 37 degr ees for bisnoryangonin and 30 degrees for hispidin formation. Molecula r weight determination by FPLC indicated that this protein has a nativ e molecular weight of ca 56-77 kDa. Styrylpyrones accumulate in rhizom es of sporophytes and gametophytes of E. arvense as major constitutive metabolites. In these organs no flavonoids could be detected. In gree n sprouts, styrylpyrone accumulation is only detected as a local respo nse to mechanical wounding or microbial attack, and flavonoids are acc umulated as major polyketide metabolites. Thus, chalcone synthase is a ctive in the sporophytes and might have developed in the course of evo lution from styrylpyrone synthase present in the more primitive gameto phytes. Copyright (C) 1996 Elsevier Science Ltd