Structural characteristics of pectic polysaccharides and arabinogalactan proteins from Heracleum sosnowskyi Manden

Polymers with different structures were isolated from the aboveground part of Heracleum sosnowskyi Manden. The sequential treatment of Heracleum with water, HCl solution, and (NH4)2C2O4 solution was observed to decrease the arabinogalactan proteins (AGP) content and increase the pectins content in the extracted polysaccharides. The linear region of the HSO-I polysaccharide having the highest yield was found to be composed mainly of partially methylesterified homogalacturonan fragments, whereas the branched region was made up of fragments of rhamnogalacturonan I whose core represents 1,2-α-l-rhamno-1,4-α-d-galacturonan. The carbohydrate side chains of the branched region are linked to the α-l-Rhap core residues via the 1,4-glycosidic bond and consist chiefly of T-β-d-Galp, 1,4-β-d-Galp and 1,6-β-d-Galp residues indicating the presence of the 1,4-β-d-galactan. NMR spectroscopy revealed the carbohydrate moiety of the AGP molecule to consist mainly of 1,3- and 1,3,6-β-d-Galp residues. The side chains comprised 1,6-β-d-Galp, terminal 4-O-Me-β-d-GlcpA, and β-d-Galp.