Abstract
To characterize the UDP-Glc: flavonoid 3-O-glucosyltransferase (3GT), which catalyze the first step to synthesis rutin, we purified it from buckwheat cotyledon. The 3GT was purified with purification folds of 171 with the final specific activities of 88.8 pmol of isoquercitrin (quercrtin-3-glucoside) generation from quercetin/min/mg protein. The 3GT was monomeric by gel filtration (56.0 KDa) and electrophoresis (58.6 KDa). The 3GT had lower Km for quercetin (sugar acceptor; 27uM) and UDP-Glc (sugar donor; 1.04 mM) than other flavonoid. Further to ascertain physiological roles of 3GT in cotyledon, changes in flavonoid concentration and 3GT activity during cotyledon growing were investigated. The 3GT activity increased parallel to rutin accumulation, and decreased rapidly after rutin concentration became maximum. On the other hand, quercetin and isoquercitrin concentration were 2 orders magnitude less than rutin concentration. It indicates that isoquercitrin generated by the 3GT would be used for rutin synthesis.
