Biomedical subjects
Publications and source records attributed to G van Nigtevecht.
This paper describes the synthesis of UDP-L-(U-14C)rhamnose from UDP-D-(U-14C)glucose and NADPH using an enzyme preparation of Nicotiana tabacum var. Xanthi. A procedure to separate UDP-l-rhamnose from the other compounds in the reaction mixture is described. Optimal separation was achieved in ethanol 95%-1 M ammonium acetate (pH 3.8) (7:3, v/v) at 30 degrees C.
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 x 10(-4) M for UDP-glucose and 0.4 x 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.
An enzyme catalyzing the transfer of the glucosyl moiety of UDP-glucose to the 5-hydroxyl group of cyanidin-3-rhamnosyl-(1 leads to 6)-glucoside has been demonstrated in petal extracts of Silene dioica plants. This glucosyltransferase activity was not detectable in green parts of these plants. The enzyme activity is controlled by a single dominant gene M; no glucosyltransferase activity could be demonstrated in petals of m/m plants. The enzyme was purified eightyfold by PVP and Sephadex G50 chromatography. The glucosyltransferase had a pH optimum of 7.4, had a molecular weight of about 55,000, was stimulated by divalent metal ions, and had a "true Km" values of 0.5 x 10(-3) M for UDP-glucose and 3.6 x 10(-3) M for cyanidin-3-rhamnosylglucoside. Pelargonidin-3-rhamnosylglucoside also could serve as acceptor. The enzyme did not catalyze the glucosylation of the 5-hydroxyl group of cyanidin-3-glucoside, although in petals of M/- n/n mutants cyanidin-3,5-diglucoside is present. ADP-glucose could not serve as a glucosyl donor.