UDP-D-Glucose: Flavonol 3 -0 - and 7-O-Glucosyl Transferases from Young Leaves of Paederia scandens var. mairei

Tw o different O -glucosyl transferases (F 3 G T and F 7 G T ) catalyzing the transfer o f D-glucose from U D P-D -glucose to the 3 and 7 positions o f flavonol, respectively, were isolated from the young leaves o f Paederia scandens var. mairei. F 3 G T and F 7 GT, which were recov­ ered in about a 1:1 ratio in the activity, were purified by about 140and 136-fold, respectively, by precipitation with am m onium sulfate fo llow ed by ion exchange chrom atography and chrom atofocusing. F 3 G T and F 7 G T both had a pH optim um o f 7.5 in Tris-HCl buffer, and an Mr o f 43 kD a. Neither F 3 G T nor F 7 G T had a M g2+ requirem ent. Both were inhibited by each 1 m M o f Zn2+, Cu2+, N -ethylm aleim ide and /7-chlorom ercuribenzoate, and both were stimulated by 14 m M 2-M E. F 3 G T and F 7 G T were different from each other in having an isoelectric point (p /) at pH 5.12 and 4.50, respectively. F 3 G T m ediated the transfer o f D-glucose exclusively to the 3-hydroxyl group o f kaem pferol and som e flavonols, but neither the 7-O -glucosides nor the 3-O -glucosides o f their flavonols were able to accept D-glucose. On the other hand, F 7 G T m ediated the transfer o f D-glucose exclusively to the 7-hydroxyl group o f kaem pferol and som e flavonols, and in addition , the 3-O -glucosides o f kaem pferol and quercetin were able to accept D-glucose though less efficiently. C onsequently, the possibility o f sequential steps o f 3 -0 and then 7-O -glucosylations o f flavonols to give the 3,7-di-O -glucoside was discussed.