UDPG: p-Coumarate glucosyltransferase activity in enzyme extracts from higher plants

Leaves of Coleus, Pilea, Cistus and Cestrum, and ripe tomatoes were all able to convert trans-cinnamic acid-[3-¹⁴C]into glucose esters of cinnamic acids. The pool sizes of these esters were measured by the radioisotopic dilution method, and they were found to be of the order of a few μg/g fresh plant material. 1-O-Caffeoyl-β-d-glucose in Cestrum leaves amounted to 70μg/g fresh plant material. Enzyme extracts from Cestrum leaves were able to convert trans-p-coumaric acid-[3-¹⁴C] to 1-O-p-coumaroyl-β-d- glucose, using UDPG as a source of glucose. This enzyme activity could be measured only by trapping techniques, due to the presence of considerable hydrolase activity in crude enzyme extracts.