title: Structure of the arabinogalactan from gum tragacanth (Astralagus gummifer).
abstract: The polysaccharide obtained by ethanol precipitation from an aqueous solution of gum tragacanth contained arabinogalactan and tragacanthic acid, as well as starch ( approximately 0.6%). GC-MS, NMR, and ESI-MS analyses showed the structure of the arabinogalactan to be even more complex than previously determined, with core structures containing Arap, beta-Araf, and alpha-Galp units, as well as known terminal, and 2-O- and 3-O-substituted alpha-Araf units. Analysis was aided by examination of free, reducing oligosaccharides present in the gum. In addition to maltose, maltotriose, maltotetraose, and maltopentaose, the following were characterized: mixed alpha-Araf (1-->2)-alpha-Araf-(1-->4)-Ara and alpha-Araf-(1-->2)-alpha-Araf-(1-->5)-Ara, which correspond to the side chains of the arabinogalactan, beta-Galp-(1-->4)-beta-Galp-(1-->4)-beta-Galp-(1-->4)-Gal; and a mixture of beta-Galp-(1-->4)-beta-Galp-(1-->4)-Gal and beta-Glcp-(1-->4)-beta-Galp-(1-->4)-beta-Galp-(1-->4)-Gal, which did not resemble side-chain structures of the arabinogalactan. The latter are suggested to be related to tragacanthic acid, which has been previously found to contain beta-Galp nonreducing end-units.
authors.affiliation: Departamento de Bioquímica, Universidade Federal do Paramá, Caixa Posta 19046, 81531-990, PR, Curitiba, Brazil. cesarat@bio.ufpr.br
authors.forename: Cesar A
authors.initials: CA
authors.lastname: Tischer
authors.forename: Marcello
authors.initials: M
authors.lastname: Iacomini
authors.forename: Philip A J
authors.initials: PA
authors.lastname: Gorin
mesh_terms: D001234:Aspergillus niger / Q000201:enzymology; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D005685:Galactans / Q000737:chemistry*; D008401:Gas Chromatography-Mass Spectrometry; D005087:Glucan 1,4-alpha-Glucosidase / Q000378:metabolism; D008745:Methylation; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D009844:Oligosaccharides / Q000032:analysis; D021241:Spectrometry, Mass, Electrospray Ionization; D014144:Tragacanth / Q000737:chemistry*
chemical_list: D005685:Galactans; D009844:Oligosaccharides; D014144:Tragacanth; D005087:Glucan 1,4-alpha-Glucosidase; C005653:arabinogalactan