UDP-Glucose: Anthocyanidin/Flavonol 3-0-Glucosyltransferase in Enzyme Preparation from Flower Extracts of Genetically Defined Lines of Matthiola incana R. Br.

In flower extracts of Matthiola incana an enzyme catalyzing the transfer of glucose from UDP-glucose to the hydroxyl group at 3-position of anthocyanidins and flavonols was demonstrated. The pH-optimum of this reaction is at pH 8.5 for pelargonidin and pH 9.5 for quercetin as substrate. The reaction is inhibited by both substrates above 10 nmol per assay. The enzyme is highly active, within 30 sec 3 nmol of 3-glucosides were formed. At 30 °C the enzyme is stable for hours and at —20 °C months. Besides UDP-glucose, TDP-glucose is a suitable glucosyl-donor, but with a reduced (70%) reaction rate. Enzyme activity is clearly inhibited by Fe²⁺and Cu²⁺ions, and by diethylpyrocarbonate. Acyanic or pale coloured mutants of several genes interfering with anthocyanin synthesis after dihydroflavonol formation show a more or less drastically reduced enzyme activity (5-40%). But none of these genes can be regarded as the structural gene for the 3-glucosyltransferase. The influence of these genes on enzyme activity and flower colour is discussed.