Étude complémentaire de la structure de trois galactoxyloglucanes (amyloïdes) de graines

Abstract

D-Galacto- D-xylo- D-glucans (amyloids) from Balsamina, Tropaeolum, and Tamarindus seeds behave in a similar manner in the presence of various glycosidase preparations: slow depolymerization by enzymes from several germinated or non-germinated seeds, and hydrolysis into monosaccharides and oligosaccharides by commercial cellulase and hemicellulase preparations from fungi. A purified cellulase from Penicillium notatum gave a dialyzable fraction almost exclusively composed of α- D-xylopyranosyl-(1→6)- D-glucose residues and a nondialyzable fraction composed of chains of β- D-(1→4)[withsome (1→3)]-glucopyranosyl residues; β- D-galacto-pyranosyl-(1→2)-α- D-xylosyl groups are linked to some of the β- D-glucosyl residues at 0-6. The presence of (1→3)-linkages in the D-glucan chain of the Balsamina was verified by methylation and sequential periodate oxidation-borohydride reduction; the distribution of the substituents on the D-glucan chain is not regular. The main D-glucan backbone, where the β- D-glucosyl residues are partly linked at 0-6 to β- D-galactosyl-(1→2)- D-xylosyl groups, is linked to D-glucan chains where almost all the D-glucose units are linked at 0-6 by one α- D-xylosyl group. The presence of 3,6-di- O-methyl- D-glucose after permethylation and hydrolysis suggests that the xyloglucan chains are linked to 0-2 of the D-glucosyl units of the galactoxyloglucan backbone.