STRUCTURES OF ENZYMATICALLY DERIVED OLIGOSACCHARIDES FROM SORGHUM GLUCURONOARABINOXYLAN

Oligosaccharides derived from alkali-extracted sorghum glucuronoarabin oxylan by digestion with a combination of (1 --> 4)-beta-D-arabinoxyla n arabinofuranohydrolase (AXH) and endo-(1 --> 4)-beta-D-xylanase (Xyl I), both from Aspergillus awamori, were purified by size-exclusion ch romatography followed by preparative high-performance anion-exchange c hromatography. Structural studies including monosaccharide analysis, m ethylation analysis,H-1 NMR spectroscopy, and mass spectrometry were c arried out, resulting in the characterisation of four novel oligosacch arides, namely, alpha-D-GlcpA-(1 --> 2)-beta-D-Xylp-(1 --> 4)-beta-D-X ylp-(1 --> 4)-beta-D-Xylp, alpha-D-GlcpA-(1 --> 2)-beta-D-Xylp-(1 --> 4)[alpha-L-Araf-(1 --> 3)]-beta-D-Xylp-(1 --> 4)-beta-D-Xylp, alpha-D- GlcpA-(1 --> 2)-beta-D-Xylp-(1 --> 4)-beta-D-Xylp-(1 --> 4)[alpha-L-Ar af-(1 --> 2)-alpha-L-Araf-(1 --> 3)]-beta-D-Xylp-(1 --> 4)-beta-D-Xylp , and alpha-D-GlcpA-(1 --> 2)-beta-D-Xylp-(1 --> 4)[alpha-L-Araf-(1 -- > 3)]-beta-D-Xylp-(1 --> 4)[alpha-L-Araf-(1 --> 2)-alpha-L-Araf-(1 --> 3)]-beta-D-Xylp-(1 --> 4)-beta-D-Xylp. The various oligosaccharides i dentified provide additional insight into the structure of sorghum glu curonoarabinoxylan. Furthermore, novel data were generated with respec t to the substrate specificity of AXH and Xyl I towards glucuronoarabi noxylans in general. (C) 1998 Elsevier Science Ltd. All rights reserve d.