Partial Purification and Some Properties of 1-Sinapoylglucose: Choline Sinapoyltransferase ("Sinapine Synthase") from Seeds of Raphanus sativus L. and Sinapis alba L.

Abstract

Abstract Hydroxycinnamoyltransferases which catalyze the formation of O-sinapoylcholine (sinapine) using 1-0-sinapoyl-β-ᴅ-glucose as acyl donor have been isolated from seeds of radish (Raphanus sativus L. var. sativus) and mustard (Sinapis alba L.) and purified 420-and 293-fold, respectively. The enzymes (“sinapine synthase”) had apparent molecular weights of about 60,000 daltons and showed highest activities at pH 7.2 and 7.6, respectively, at 45 °C with apparent energies of activation at 53 kJ mol-1. There were no requirements for divalent cations or sulfhydryl reagents. The apparent Km’s of the radish and mustard enzymes were 0.48 and 0.71 mᴍ for 1-sinapoylglucose and 5.3 and 6.5 mᴍ for choline, respectively. The ratios of the Vmax/Km values for 1-sinapoyl-1-feruloyl- and 1-p-coumaroylflucose were found to be 100:19:19 (radish) and 100:20:29 (mustard). 6-0-Sinapoylglucose, 3-0-sinapoylfructose, 1-0-benzoyl- and 1-0-galloylglucose were not accepted as donors.