Identification and properties of UDP-glucose: Cyanidin-3-O-glucosyltransferase isolated from petals of the red campion (Silene dioica)

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Abstract
An enzyme catalyzing the transfer of the glucosyl moiety of UDP-glucose to the 3-hydroxyl group of cyanidin has been demonstrated in petal extracts of Silene dioica mutants with cyanidin-3-O-glucoside in the petals. This transferase activity was also present in young rosette leaves and calyces of these plants. The highest glucosyltransferase activity was found in petals of opening flowers of young plants. The enzyme was purified ninetyfold by PVP and Sephadex chromatography. The glucosyltransferase had a pH optimum of 7.5, had a “true Km value” of 4.1×10−4 m for UDP-glucose and 0.4×10−4 m for cyanidin chloride, and was not stimulated by divalent metal ions. Both p-chloromercuribenzoate and HgCl2 inhibited the enzyme activity. Pelargonidin chloride and delphinidin chloride at reduced rates also served as substrates. The enzyme did not catalyze the glucosylation of the 3-hydroxyl group of flavonols or the 5-hydroxyl group of anthocyanins. ADP-glucose could not serve as a glucosyl donor. The results of Sephadex G150 chromatography suggest that the glucosyltransferase can exist as dimer of about 125,000 daltons and as active monomers of 60,000 daltons. The genetic control of the glucosyltransferase activity is discussed.