Hydroxycinnamoyl: coenzyme A transferase involved in the biosynthesis of kaempferol-3-(p-coumaroyl triglucoside) in Pisum sativum.

The major flavonoids of Pisum are derivatives of kaempferol and quercetin, including both triglucosides and acylated triglucosides in which the acyl group is p-coumaric acid. Although hydroxycinnamic acid esters of flavonoids are common pigments in many plants, neither the enzymes nor the precursors involved in their biosynthesis have been demonstrated. We report here that crude enzyme preparations extracted from peas catalyze the transfer of the p-coumaroyl moiety of p-coumaroyl:Coenzyme A to kaempferol-3-triglucoside forming kaempferol-3-(p-coumaroyl triglucoside) as the acylated product. The reaction product has been vigorously shown to be identical to the naturally occurring kaempferol-3-(p-coumaroyl triglucoside) in both chromatographic and chemical properties. The enzymatic formation of the acylated derivative occurred only minimally when incubated with the cofactors required for carboxyl group activation (ligase) and maximally when incubated with p-coumaroyl : Coenzyme A as the acyl donor.