| This dissertation describes the elucidation of part of the primary structure of the plant cell wall pectic polysaccharide rhamnogalacturonan II. Rhamnogalacturonan II may be the most structurally complex plant polysaccharide ever isolated. Rhamnogalacturonan II is composed of at least ten different monosaccharides interconnected by at least 20 different glycosidic linkages.;Selective acid hydrolysis of apiosyl glycosidic linkages of rhamnogalacturonan II was used to generate a mixture of oligosaccharides for structure analysis. A heptasaccharide was purified to homogeneity by gel-filtration and anion-exchange chromatography of partially hydrolyzed rhamnogalacturonan II. Apiose was at the reducing end of the heptasaccharide. The heptasaccharide was found to contain, in addition to 3('1)-linked apiose, terminal L-rhamnopyranosyl, terminal (2-O-methyl)-L-fucopyranosyl, 2-linked L-arabinopyranosyl, 2,4-linked D-galactopyranosyl, 2-linked L-acerofuranosyl, and 3-linked L-rhamnopyranosyl residues. The sequence of these glycosyl residues was determined by forming and characterizing overlapping partially O-deuteriomethylated, partially O-deuterioethylated oligosaccharide-alditols from the heptasaccharide. Some of the heptasaccharide molecules were found to be mono- and di-O-acetylated.;All aspects of the primary structure of the heptasaccharide were determined except the absolute configuration of the apiose and the point of attachment of O-acetyl esters. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI;A branched-chain acidic sugar, 3-C-carboxy-5-deoxy-L-xylose, was isolated by anion-exchange chromatography of acid-hydrolized rhamnogalacturonan II. The sugar was shown to be a carboxyl-branched deoxy-pentose by nuclear magnetic resonance spectroscopy and mass spectrometry of the isolated sugar and of several derivatives. X-ray crystallography of one of the derivatives revealed that the sugar had the xylo configuration. The sugar was shown to have the L absolute configuration by the identification of L-lactic acid as the major product of periodate oxidation of the anomeric mixture of methyl glycosides. This is the first report of a naturally occurring branched-chain acidic monosaccharide. "Aceric acid" has been proposed as a trivial name for 3-C-carboxy-5-deoxy-L-xylose. |
