title: A xylosyltransferase that synthesizes beta-(1-->4)-xylans in wheat (Triticum aestivum L.) seedlings.
abstract: A particulate preparation from 6-day-old seedlings of wheat (Triticum aestivum L.) was found to contain a xylosyltransferase (XylTase) which incorporated xylose (Xyl) from UDP-xylose into exogenous beta-(1-->4)-xylooligosaccharides with 2-aminopyridine-derivatized reducing end groups. High-performance liquid chromatographic analysis showed that the chain elongation of pyridylaminated beta-(1-->4)-xylotriose (Xyl3-PA) occurred by attachment of a series of one, two, or three xylosyl residues, depending on substrate concentrations and reaction times. Methylation analysis and beta-xylosidase digestion of the newly synthesized Xyl4-PA confirmed that the xylosyl residues were incorporated through beta-(1-->4)-linkages. The enzyme was maximally active at pH 6.8 and 20 degrees C, and required Triton X-100, which enhanced activity 5-fold at a concentration of 0.05-2%. Divalent ions, including Mn2+ and Mg2+, did not affect activity. Enzyme activity increased with increasing polymerization of xylosyl residues of the acceptor substrates: for instance, Xyl5-PA was almost 7 times as efficient as Xyl2-PA. The apparent Michaelis constants of the enzyme for Xyl3-PA and UDP-xylose were 13.5 and 7.9 mM, respectively. The enzyme also catalyzed incorporation of radioactive sugars (Xyl together with a small portion of L-arabinose) from UDP-[14C]xylose into higher beta-(1-->4)-xylooligosaccharides (degree of polymerization > 7) with or without (4-O-methyl-)glucuronosyl side chains at activities comparable to those observed for pyridylaminated xylooligosaccharides, and into several heteroxylans but with much lower efficiency. Enzymatic hydrolysis of the product with a beta-xylanase degraded it into mainly xylobiose, providing further evidence that the xylosyl residues are incorporated through beta-(1-->4)-linkages.
authors.affiliation: Department of Biochemistry and Molecular Biology, Faculty of Science, Saitama University, Urawa, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Kuroyama
authors.forename: Y
authors.initials: Y
authors.lastname: Tsumuraya
mesh_terms: D002473:Cell Wall / Q000737:chemistry; D008861:Microsomes / Q000201:enzymology; D010430:Pentosyltransferases / Q000378:metabolism* / Q000493:pharmacokinetics; D018520:Plant Shoots / Q000201:enzymology; D011134:Polysaccharides / Q000096:biosynthesis; D013379:Substrate Specificity; D014908:Triticum / Q000201:enzymology*; D014990:Xylans / Q000096:biosynthesis*; D000097608:UDP Xylose-Protein Xylosyltransferase
chemical_list: D010430:Pentosyltransferases; D011134:Polysaccharides; D014990:Xylans; D000097608:UDP Xylose-Protein Xylosyltransferase; C007916:hemicellulose; C074948:(1-4)-xylan; C038331:1,4-beta-D-xylan synthase