The extracellular polysaccharide of Porphyridium sp.:: an NMR study of lithium-resistant oligosaccharidic fragments

This study deals with the chemical characterization of an extracellular polysaccharide produced by the unicellular red alga Porphyridium sp. The sugar moiety of this polymer is composed of three neutral monosaccharides (Xyl, Glc, and Gal) and one uronic acid (GlcA). Proteins represent 5.5% of the dry weight of the polymer. Uronic degradation of this exopolysaccharide with lithium in ethylenediamine yielded two different oligosaccharides. The absolute configuration of the constitutive monosaccharides was chemically determined and revealed the presence of D-Xyl, D-Glc, D-, and L-Gal. The following oligosaccharide structures were established by NMR spectroscopy: beta-D-Xylp 1 down arrow 2 beta-D-Xylp-(1-->4)-beta-D-Xylp-(1-->4)-L-Galp and beta-D-Xylp 1 down arrow 2 beta-D-Galp-(1-->3)-beta-D-Glcp-(1-->3)-beta-D-Xylp-(1-->4)-beta-D-Xylp-(1-->4)-L-Galp (C) 2003 Elsevier Ltd. All rights reserved.