The 2″-O-glucosylation of vitexin and isovitexin in petals of Silene alba is catalysed by two different enzymes |
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Authors: | Ria Heinsbroek Jan Van Brederode Gerrit Van Nigtevecht Jan Maas John Kamsteeg Elisabeth Besson Jean Chopin |
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Institution: | 1. Rijksuniversiteit Utrecht, Vakgroep Populatie en Evolutie Biologie, Padualaan 8 Utrecht, 3584 CH, The Netherlands;2. Laboratoire de Chimie Biologique, Université de Lyon, 69622, Villeurbanne, France |
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Abstract: | Two separate genes, Fg and Vg, which govern the presence of isovitexin 2″-O-glucoside and vitexin 2″-O-glucoside respectively in the petals of Silene alba control different glucosyltransferases. In Vg/Vg,fg/fg plants no isovitexin 2″-O-glucosyltransferase was present and in vg/vg,Fg/Fg plants no vitexin 2″-O-glucosyltransferase activity could be detected. The Fg-controlled UDP-glucose: isovitexin 2″-O-glucosyltransferase has a pH optimum of8.5, while the Vg-controlled vitexin 2″- O-glucosyltransferase has a pH optimum of7.5. Both glucosyltransferases are stimulated by the divalent cations Ca2+, Co2+, Mn2+ and Mg2+. For isovitexin 2″-O-glucosylation, however, much higher concentrations are needed than for vitexin 2″-O-glucosylation.For UDP-glucose a ‘true Km’ value of0.3 mM with the Fg-controlled and of 0.2 mM with the Vg-controlled enzyme was found. For isovitexin and vitexin these values are respectively 0.09 and 0.01 mM. |
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Keywords: | Caryophyllaceae MS fragmentation glucosyltransferases biosynthesis |
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