Structural characterization of a tobacco rhamnogalacturonan

Abstract

A rhamnogalacturonan, extracted with hot water from the aqueous ethanol insoluble residue of flue-cured bright tobacco lamina, was purified by tangential flow ultrafiltration, ion chromatography and gel filtration. It was characterized by chemical and spectroscopic methods. Fractionation revealed that the rhamnogalacturonan consisted of a series of polysaccharides with different amounts of methyl-esterified galactopyranosyluronic acid residues in the backbone and different amounts of neutral sugar residues. The main pectic polysaccharide fraction has a backbone consisting of 4-linked α- d-galactopyranosyluronic acid residues interspersed with 2-linked l-rhamnopyranosyl residues. Approximately 22% of the galactopyranosyluronic acid residues are methylated. The main chain is branched at C-4 of rhamnose with neutral sugar side chains containing terminal and 4-linked β- d-galactopyranosyl and terminal and 5-linked α- l-arabinofuranosyl residues. The average degree of polymerization of this tobacco rahamnogalacturonan was estimated to be 400.