Structural investigation of a galactoglucomannan from cell walls of tobacco ( Nicotiana tabacum) midrib

Abstract

Cell-wall polysaccharides of the midrib of Nicotiana tabacum were fractionated into pectin, hemicellulose, and α-cellulose components. From the α-cellulose fraction, a polymer composed of d-galactose, d-glucose, and d-mannose in the molar ratios ∼1:2:4 was extracted by aqueous 25% sodium hydroxide-5% boric acid and purified by barium hydroxide precipitation, ion-exchange chromatography, and gel filtration. Methylation analysis, enzymic degradation, and 13C-n.m.r. studies showed that the polysaccharide was built up of (1→4)-linked β- d-glucopyranosyl and β- d-mannopyranosyl residues in the molar ratio ∼1:2, and that ∼14% of the d-mannosyl residues were substituted at O-6 by α- d-galactopyranosyl or 2- O-β- d-galactopyranosyl-α- d-galactopyranosyl side-chains.