Styrylpyrone biosynthesis in Equisetum arvense

Styrylpyrone synthase was detected in cell free extracts from gametophytes 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 characterized in partially purified protein extracts. p-Coumaroyl-CoA was accepted as substrate at pH 6.0-8.5 in various buffer systems with the formation of bisnoryangonin, and optimum enzyme activity was observed in potassium phosphate buffer at pH 7.5. Caffeoyl-CoA was accepted as substrate only in potassium phosphate buffer at pH 6.0-7.5 with formation of hispidin; optimum enzyme activity was observed at pH 7.0. The apparent K-m values were 220 mu M for caffeoyl-CoA and 230 mu M for p-coumaroyl-CoA. The temperature optimum of the enzyme activity was 37 degrees for bisnoryangonin and 30 degrees for hispidin formation. Molecular weight determination by FPLC indicated that this protein has a native molecular weight of ca 56-77 kDa. Styrylpyrones accumulate in rhizomes of sporophytes and gametophytes of E. arvense as major constitutive metabolites. In these organs no flavonoids could be detected. In green sprouts, styrylpyrone accumulation is only detected as a local response to mechanical wounding or microbial attack, and flavonoids are accumulated as major polyketide metabolites. Thus, chalcone synthase is active in the sporophytes and might have developed in the course of evolution from styrylpyrone synthase present in the more primitive gametophytes. Copyright (C) 1996 Elsevier Science Ltd