UDP-GLUCOSE - FLAVONOID O-GLUCOSYLTRANSFERASE FROM STRAWBERRY FRUIT

An enzyme catalysing the glucosylation of quercetin at the 7-hydroxyl group using uridine diphosphate-D-glucose (UDPGlc) as the glucosyl donor was partially purified ca 100-fold from ripening strawberry (Fragaria ananassa Duch. cv Tillikum) fruit. The apparent K-m values for UDPGlc and quercetin were 0.14 and 0.04 mM, respectively. The optimum pH of 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. Flavonoids glucosylated included flavonols, flavonones and a flavone, but the highest activity was observed with the isoflavone, biochanin A.