Involved in the production of glucuronosylated anthocyanins that are the origin of the red coloration of flowers. Can use cyanidin 3-O-6''-O-malonylglucoside, cyanidin 3-O-glucoside and delphinidin 3-O-glucosideas substrates, but not pelargonidin 3-O-glucoside, cyanidin 3-O-3'',6''-O-dimalonylglucoside, pelargonidin 3,5-O-diglucoside, pelargonidin 3-O-6''-O-malonylglucoside-5-O-glucoside, quercetin 3-O-glucoside, quercetin 3-O-6''-O-malonylglucoside, daidzin, genistin,7-O-6''-O-malonylglucosides of daidzein and genistein, cyanidin, quercetin, daidzein, genistein p-Nitrophenyl beta-D-glucopyranoside, beta-estradiol, 17alpha-estradiol, 1-naphthol, 2-naphthol, 4-methylumbelliferone, and p-nitrophenol. Highly specific for UDP-glucuronate (UDP-GlcUA). Arg-25 is decisive with respect to UDP-sugar specificity. cyanidin 3-O-beta-D-glucoside + UDP-alpha-D-glucuronate = cyanidin 3-O-(2-O-beta-D-glucuronosyl)-beta-D-glucoside + H(+) + UDP Inhibited by copper, mercury, UDP, UTP and partially by calcium, cadmium, iron and UMP. Not affected by cobalt, magnesium, manganese, zinc, nickel, tin, uridine, sadium malonate and glucose. Optimum pH is 8.0. Optimum temperature is 35 degrees Celsius. Monomer. Expressed in petals. Not detected in sepals, stems, leaves, tubular corollas and white petals. Peak of expression at stage 4 of flower development. Belongs to the UDP-glycosyltransferase family.