UDP-Glucose: Cyanidin 3-O-glucosyltransferase from red cabbage seedlings

An enzyme, catalysing the glucosylation of cyanidin at the 3-position using uridine diphosphate-D-glucose (UDPG) as glucosyl-donor, has been isolated and purified about 50-fold from young red cabbage (Brassica oleracea) seedlings. The pH optimum for this reaction was ca 8 and no additional cofactors were required. The reaction was inhibited by cyanidin (above 0.25 mM) and by very low concentrations of the reaction product cyanidin-3-glucoside (5 μM). The K_m values for UDPG and cyanidin were 0.51 and 0.4 mM respectively. In addition to cyanidin the enzyme could also glucosylate the following compounds at the 3-position: pelargonidin, peonidin, malvidin, kaempferol, quercetin, isorhamnetin, myricetin and fisetin. In contrast, cyanidin-3-glucoside, cyanidin-3-sophoroside, cyanidin-3,5-diglucoside, apigenin, luteolin, naringenin and dihydroquercetin were not glucosylated.