Enzymic Dissociation of Zea Shoot Cell Wall Polysaccharides : IV. Dissociation of Glucuronoarabinoxylan by Purified Endo-(1 --> 4)-beta-Xylanase from Bacillus subtilis

The structure of a glucuronoarabinoxylan in Zea mays L. (hybrid B73 x Mo17) shoot cell walls has been studied. The water-insoluble fraction of Zea shoot cell walls, pretreated with purified Bacillus subtilis (1 --> 3), (1 --> 4)-beta-d-glucan 4-glucanohydrolase, was treated with purified B. subtilis endo-(1 --> 4)-beta-xylanase. Carbohydrates (2.6% of the waterinsoluble fraction of Zea shoot cells walls) derived from the enzyme treatment consisted of glucuronoarabinoxylan fragments with molecular weights which varied from a few hundred to over 2.0 x 10(5) daltons. Structural analyses of the fragments suggested that the glucuronoarabinoxylan had a xylan backbone which contained (1 --> 4)-beta-d-xylopyranosyl residues, with about 60 to 70% substitution at the C-2 or C-3 position with arabinose, glucuronic acid, and other substituents. Furthermore, the glucuronoarabinoxylan contained a phenolic component which appeared to be primarily ferulic acid bonded to carbohydrate, probably by an ester linkage. The amount of ferulic acid was approximately 3 micrograms per 100 micrograms of carbohydrate.