Partial Purification and Some Properties of a Hydroxycinnamoyl Glucosyltransferase from Tomato Fruits

A glucosyltransferase was isolated from immature “cherry” tomatoes and was partially purified (200-fold) by ammonium sulphate precipitation and successive chromatography on Sephadex G-100 and DEAE-cellulose columns. The enzyme utilised the free hydroxycinnamic acids and UDP-glucose in the formation of their respective glucosides (pH 8.0) and glucose esters (pH 7.0); but did not accept the CoA thiolesters of HCAs in the presence of glucose-1-phosphate. The constant glucoside/glucose ester ratio observed during purification suggests that both reactions are catalysed by the same enzyme. The K m values for /»-coumaric, caffeic, ferulic and sinapic acids were 0.8, 1.5, 1.4 and 2.5 hm, respectively. With ferulic acid as substrate, the K m value for UDPG was 10 hm. The enzyme required an -S H group for activity and the reaction was strongly inhibited by EDTA, divalent metal ions and UDP.