Further Structural Study of the Barley and Bamboo Shoot Xyloglucans by Xyloglucanase

Abstract

To investigate the arrangement of the glucose residues which are not xylosylated at O-6 in the β-1,4-D-glucan backbone of xyloglucan from Gramineae, a xyloglucan from immature barley plants was hydrolyzed by a purified Geotrichum sp. M128 xyloglucan specific endo-1,4-β-D-glucanase (xyloglucanase). The fragment oligosaccharides were then analyzed by matrix-assisted laser-desorption ionization time of the flight mass spectrometry before and after treatment with an oligoxyloglucan-specific glycosidase, oligoxyloglucan reducing end-specific cellobiohydrolase from Geotrichum sp. M128, with a mixture of isoprimeverose-producing oligoxyloglucan hydrolase from Eupenicillium sp. M9 and β-D-glucosidase from Trichoderma viride, or with β-D-galactosidase from Bacillus circulans. Tetra-, penta-, hexa-, hepta-, octa- and nona-saccharide fractions were obtained as major oligosaccharide fractions, which might be composed of XX, of XXG, of XXGG, of XXGGG and LXGG, of XLGGG, LXGGG, XXGGGG and GXXGGG, and of XLGGGG, LXGGGG, GXLGGG, GLXGGG and XXGGGGG, respectively. In addition, the oligosaccharide units of bamboo shoot xyloglucan were analyzed. The structure of bamboo shoot xyloglucan was shown to be very similar to that of barley xyloglucan. These results suggest that the Gramineae xyloglucan has regions consisting of two, three, four and five contiguous glucose residues which are not xylosylated at O-6 in the β-1,4-D-glucan backbone.