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'Gossypetin' in keywords Facet   Publication Year 1997  [X]
Facet   section ZfN Section C  [X]
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1Author    K. Stich3, H. Halbwirth3, F. Wurst3, G. ForkmannbRequires cookie*
 Title    UDP-GIucose: Flavonol 7-O-glucosyItransferase Activity in Flower Extracts o f Chrysanthemum segetum  
 Abstract    The yellow colour of Chrysanthemum segetum petals is due to the presence o f the 7-0-glucosides of quercetin and particularly gossypetin (8-hydroxyquercetin). In petal extracts of C. segetum an enzyme was demonstrated which catalyzes the transfer o f the glucosyl moiety o f uridine 5'-diphosphoglucose (U D P G) to the 7-hydroxyl group of flavonols with gossypetin and quercetin as the best substrates. Besides flavonols flavanones and flavones were found to be glucosylated in the 7-position. The pH-optimum of the reaction highly depended on the substrate used. With quercetin as substrate, maximal enzyme activity occurred at a pH o f 8.25 and a temperature of 25 °C, but 7-O-glucosylation also proceeded at low temper­ atures. Studies on temperature stability revealed, that there was no influence on the glucosy-lation reaction up to 40 °C. Higher temperatures led to a loss of enzyme activity. Using gossypetin as a substrate a similar course of temperature stability was observed. Addition of M g2+, Ca2+ and K C N slightly stimulated 7-O-glucosylation, whereas C o2+, Cu2+, Fe2+, Hg2+, p-hydroxymercuribenzoate and N-ethylmaleimide showed a strong inhibitory effect. Addi­ tional enzymatic studies were performed with the commercial strain " Stern des Orients" where gossypetin 7-O-glucoside is restricted to the inner parts of the petals. For enzyme extracts from both parts of the petals gossypetin was found to be the most attractive sub­ strate. In comparison to quercetin (133.4 [.ikat / kg protein) an about three times higher specific activity of the 7-0-glucosyltransferase(s) was determined with gossypetin (382.1 (.ikat/ kg protein) as substrate, indicating that hydroxylation o f quercetin in 8-position to gossypetin precedes 7-O-glucosylation. 
  Reference    Z. Naturforsch. 52c, 153—158 (1997); received November 11/ 
  Published    1997 
  Keywords    Chrysanthemum segetum, UDP-Glucose: Flavonol 7-O-glucosyltransferase, Quercetin, Gossypetin, Flavonoids 
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 TEI-XML for    default:Reihe_C/52/ZNC-1997-52c-0153.pdf 
 Identifier    ZNC-1997-52c-0153 
 Volume    52