<jats:p>Protein preparations from Arabidopsis thaliana and Brassica rapa catalyzed the formation of O-sinapoyl-ʟ-malate using 1-O-sinapoyl-β-glucose as acyl donor. The enzyme involved, 1-O-sinapoyl-β-glucose :ʟ-malate O-sinapoyltransferase (SMT; EC 2 .3 .1 .-), catalyzes in the cotyledons of the seedlings the key step in the conversion of the seed constituent sinapine (O-sinapoylcholine) to sinapoylmalate by way of the intermediate sinapoylglucose.