UDP-Glucose: Cyanidin 3-O-glucosyltransferase from cell cultures of Haplopappus gracilis

From cell cultures of Haplopappus gracilis, an enzyme, catalyzing the glucosylation of cyanidin at the 3 position using uridine diphosphate-D-glucose (UDPG) as glucosyl-donor, has been isolated and purified 50-fold. The enzyme was not specific for cyanidin alone, but also glucosylated other anthocyanidins and flavonols in position 3. However, apigenin, luteolin, naringenin and dihydroquercetin were not glucosylated. The reaction has an optimum pH of approximately 8, and the apparent K m values for UDPG and cyanidin were 0.5 and 0.33 mM respectively. The enzyme reaction is strongly inhibited by cyanidin (above 0.25 mM).