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1Author    Nariyuki Ishikura, Zhi-Qing YangRequires cookie*
 Title    UDP-D-Xylose: Flavonol 3-O-Xylosyltransferase from Young Leaves of Euonymus alatus f. ciliato-dentatus  
 Abstract    From the young leaves of Euonymus alatus f. ciliato-dentatus, a novel enzyme, UDP-D-xylose: flavonol 3-O-xylosyltransferase (F 3 X T), catalyzing the transfer o f D-xylose from UDP-D-xylose to the 3 position o f 3,5,7,4'-tetrahydroxyflavone (kaempferol), was detected and purified about 16-fold by precipitation with am m onium sulfate and DEAE-cellulose CC, by which F 3 X T was separated from two coexisting flavonol O-glucosyltransferases (FGT). Thus, F 3 XT was isolated as a soluble enzyme with a pH optim um o f 7.0 in Tris-HCl buffer. The molecular weight o f F 3 X T , which had an isoelectric point at pH 6.1, was estimated by elution from a column o f Sephadex G-100 to be about 48 kDa. The activity o f F 3 X T was stimulated by 14 mM 2-ME and strongly inhibited by 1 mM C u 2+, 1 mM Z n 2+, and various re­ agents that react with sulfhydryl groups. Am ong the substrates tested for F 3 X T , kaempferol was the best. The Km values for kaempferol and UDP-xylose were determined to be 0.83 jim and 25 |iM, respectively. F 3 X T mediated the transfer o f xylose exclusively to the 3-hydroxyl group o f kaempferol. Isorhamnetin, quercetin and fisetin also can function as xylosyl acceptor though less efficiently, but neither the 7-O-glucosides nor the 3-O-glucosides o f kaempferol and quercetin were able to accept D-xylose. Dihydroflavonols were not xylosylated. 
  Reference    Z. Naturforsch. 46c, 1003—1010 (1991); received February 28/June 28 1991 
  Published    1991 
  Keywords    Celastraceae, Euonymus, Flavonol, O-Xylosyltransferase, Characterization 
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 TEI-XML for    default:Reihe_C/46/ZNC-1991-46c-1003.pdf 
 Identifier    ZNC-1991-46c-1003 
 Volume    46