An enzyme catalysing the glucosylation of quercetin at the 7-hydroxyl
group using uridine diphosphate-D-glucose (UDPGlc) as the glucosyl don
or was partially purified ca 100-fold from ripening strawberry (Fragar
ia ananassa Duch. cv Tillikum) fruit. The apparent K-m values for UDPG
lc and quercetin were 0.14 and 0.04 mM, respectively. The optimum pH o
f this glucosylation reaction was 7.5. Enzymatic activity was slightly
stimulated by Ca2+ and Mg2+, but was completely inhibited by Cu2+ and
p-chloromercuribenzenesulphonic acid (PCMBS). A M(r) of ca 55 000 was
determined by gel filtration. The substrate specificity was broad. Fl
avonoids glucosylated included flavonols, flavonones and a flavone, bu
t the highest activity was observed with the isoflavone, biochanin A.