A highly substituted glucuronoarabinoxylan from developing maize coleoptiles

Abstract

A glucuronoarabinoxylan in which about six of every seven xylosyl residues were substituted with terminal arabinofuranosyl and glucosyluronic groups was extracted from developing maize coleoptiles with dilute alkali and purified by gel-permeation chromatography. Terminal arabinofuranosyl groups attached mostly to O-3 of the xylan backbone constituted most of the substitution. Indirect double-methylation analysis of mild acid-hydrolyzed xylan, direct methylation analyses of carbodiimide-activated, NaBH 4-reduced uronic acid groups, and isolation of the glucosyluronic-xylose aldobiouronic acids followed by 2-D COSY 1H-n.m.r. spectroscopy indicated that most, if not all, of the d-glucosyluronic groups were α-(1→2)-linked to the xylan. Smith degradation indicated that at least a portion of this highly substituted xylan may have a repeating-unit structure.