Uronic acid constituents of oat-coleoptile cell walls

Abstract

Uronic acids were obtained from polysaccharides of oat-coleoptile cell walls by acid hydrolysis, and were separated chromatographically. They were identified by hydrolysis, by comparison with similar compounds from maize-cob hemicellulose B and, for the major components, by reduction to the correspondong sugar or disaccharide. The products included free hexuronic acids (mainly galacturonic acid, small amounts of glucuronic acid and methylglucuronic acid), a number of aldobiouronic acids and aldotriouronic acids (principally glucuronosylxylose and 4-O-methyl-glucuronosylxylose, smaller amounts of glucuronosylxylosylxylose, methylglucuronosylxylosylxylose, glucuronosylgalactose and galac-turonosylrhamnose) and galacturonosylgalacturonic acid. Evidence was obtained that indicates that the principal aldobiouronic acids have (1- 2)-linkage. Extraction with hot dilute mineral acid removed hemicelluloses that contain glucuronic acid and methylglucuronic acid, but removed only a fraction of the galacturonic acid. The remainder of the galacturonic acid could be obtained by pectinase treatment. Pectinase treatment alone removed only a minor proportion of the cell-wall glucuronic acid and methylglucuronic acid. By extraction with both hot acid and pectinase the uronic anhydride content of oat-coleoptile cell-wall material was found to be about 5%, of which about 2/3 is galacturonic acid and 1/3 glucuronic acid and 4-O-methylglucuronic acid.