THE STRUCTURE OF PLANT-CELL WALLS .30. STRUCTURAL CHARACTERIZATION OF AN ARABINOSE-CONTAINING HEPTADECASACCHARIDE ENZYMATICALLY ISOLATED FROM SYCAMORE EXTRACELLULAR XYLOGLUCAN

An arabinose-containing heptadecasaccharide, generated by endoglucanase digestion of the xyloglucan secreted by suspension-cultured sycamore cells, was structurally characterized. The structure of the heptadecasaccharide was unambiguously determined through combined data generated by 1H-n.m.r. spectroscopic, fast-atom bombardment mass spectrometric, and glycosyl-composition and glycosyl-linkage analyses of the intact heptadecasaccharide and of oligosaccharide fragments of the heptadecasaccharide. 1D and 2D 1H-n.m.r. analyses provided data for assignment of the anomeric configurations of the glycosidic linkages, as well as information about the glycosylic and linkage compositions of the heptadecasaccharide. F.a.b.-m.s. data provided the molecular weight and supplied critical information about the glycosylic composition and glycosylic sequence of the heptadecasaccharide. The heptadecasaccharide was found to be a combination of previously characterized nona- and hepta-saccharide components of xyloglucan. The nonasaccharide was shown to be glycosidically linked to the heptasaccharide through C-4 and the β-glucosyl residue nearest to the nonreducing end of the heptasaccharide component. An arabinosyl residue was glycosidically linked at C-2 of the same β-glucosyl residue at the non-reducing end of the heptasaccharide component of the heptadecasaccharide. Although the presence of arabinosyl residues in sycamore xyloglucan has been recognized since 1973, the location of the arabinosyl residues had not been ascertained. © 1990.