Malonyl-coenzyme A: Anthocyanidin 3-glucoside malonyltransferase from flowers of Callistephus chinensis

In flowers of Callistephus chinensis containing malonylated pelargonidin 3-glucoside, an enzyme was demonstrated which catalyses the transfer of the malonyl moiety from malonyl-CoA to the 3-glucosides of pelargonidin, cyanidin and delphinidin and with a considerably lower reaction rate also to cyanidin 3,5-diglucoside. Besides malonyl-CoA, a range of other dicarboxylic acids serve as acyl donors but to a lesser extent. The enzyme exhibits a sharp pH-optimum at 7.0 and a temperature optimum of 50°. The reaction does not require additional co-factors and is inhibited by divalent cations and by several inhibitors of enzymic reactions, in particular by p-chloromercuribenzoate. The possible significance of malonylation of anthocyanins for their transport into the vacuole is discussed.