ENZYMATIC DISSOCIATION OF ZEA SHOOT CELL-WALL POLYSACCHARIDES .5. DISSOCIATION OF XYLOGLUCAN BY UREA

A procedure has been devised to extract and identify structural components of the xyloglucan of Zea mays L. (hybrid B73 X Mo17) shoot cell-walls. A water-insoluble fraction of Zea shoot cell-walls, after pretreatment with purified Bacillus subtilis (1 --> 3),(1 --> 4)-beta-D-glucan 4-glucanohydrolase, purified B. subtilis endo-(1 --> 4)-beta-xylanase and an enzyme preparation from B. subtilis enriched in glucuronoxylanase (Kato and Nevins 1984a, Nishitani and Nevins 1991), was subsequently treated with 7 M urea. The carbohydrates (0.8% of the water-insoluble fraction of Zea shoot cell-walls) liberated by the urea treatment, were comprised of xyloglucan polymers with molecular weights which varied from 1.0 X 10(4) to 4.0 X 10(4) Da. Other wall fragments associated with the isolated polymer suggest covalent bonding of xyloglucan to other polysaccharides. Structural analyses of the xyloglucan polymers reveal a cellulose-like backbone with about 35% of the C-6 positions substituted with xylose and other sugars. About 80% of xyloglucan present in the enzyme-pretreated water-insoluble fraction of Zea shoot cell-walls was liberated by the urea treatment. The procedure avoids the use of alkali in the solubilization of xyloglucan.