Pectic polysaccharide rhamnogalacturonan II is covalently linked to homogalacturonan

Phytochemistry. 2001 Jul;57(6):969-74. doi: 10.1016/s0031-9422(01)00047-4.


A borate-containing pectin was solubilized from sugar beet (Beta vulgaris L. ) cell walls by treatment with 0.5 M imidazole, pH 7. The molecular weight of the pectin was reduced when the borate ester was hydrolyzed by treatment with 1 N HCl. Treatment of the acid-treated pectin with boric acid in the presence of Pb(2+) gave a product whose molecular weight distribution was similar to the imidazole-soluble pectin. The imidazole-soluble pectin was saponified and then digested with endo- and exo-polygalacturonases. These treatments shifted the boron peak at the high molecular weight region to the low molecular weight (10 kDa), which corresponds to rhamnogalacturonan II-borate ester cross-linked dimer (dRG-II-B). The treatment also generated rhamnogalacturonan I (RG-I), dRG-II-B, monomeric rhamnogalacturonan II and galacturonic acid. These results show that imidazole solubilizes a high molecular weight borate-containing pectic complex composed of homogalacturonan-rhamnogalacturonan II and RG-I. Our data suggest that borate esters formed between rhamnogalacturonan II molecules cross-link the macromolecular pectin.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Borates
  • Cell Wall / chemistry
  • Chenopodiaceae / chemistry*
  • Chromatography, Gel
  • Chromatography, High Pressure Liquid
  • Dimerization
  • Hydrolysis
  • Molecular Weight
  • Monosaccharides / analysis
  • Pectins / chemistry*
  • Pectins / isolation & purification
  • Polygalacturonase


  • Borates
  • Monosaccharides
  • rhamnogalacturonan II
  • Pectins
  • Polygalacturonase
  • polygalacturonic acid