Two flavonoid-specific malonyltransferases from cell suspension cultures of Petroselinum hortense: Partial purification and some properties of malonyl-coenzyme A: Flavone/flavonol-7-O-glycoside malonyltransferase and malonyl-coenzyme A: Flavonol-3-O-glucoside malonyltransferase

Two malonyltransferases were isolated from irradiated cell suspension cultures of parsley (Petroselinum hortense) and extensively purified. One enzyme was most active with flavone and flavonol 7-O-glycosides as substrates; the other enzyme preferentially malonylated flavonol 3-O-glucosides. The substrate specificity of the enzymes in vitro was in good agreement with the pattern of malonylated flavonoid glycosides occurring in the cell cultures in vivo. The apparent K_m values for the most efficient substrates, including the donor of the acyl residue, malonyl-CoA, were about 4–20 μm. Both malonyltransferases had an apparent molecular weight of approximately 50,000.