Structural investigations on polysaccharides of the chlorophyceae

Abstract

Structural studies on the hot water-soluble starch-free polysaccharide extract from the green alga, Cladophora rupestris. 1. Cel column chromatography, gel electrophoresis., and ultrafiltration,gave no significant fractionation of the above material into homopolymeric species. 2. Three sequential Smith's degradations of the polysaccharide and quantitative analysis by gas liquid chromatography of the hydrolysates of both the polymeric materials and fragments has established the mutual linkage of the individual sugar units; confirmed that all the xylose and some of the galactose units are present on the peripheryof the molecule; and provided additional information on the overall structure of the macromolecule. A novel mild hydrolysis technique was developed. Gel column chromatography gave a measure of the degree of cleavage occurring in the polymeric materials. 3. Autohydrolysis resulted in the isolation and characterisation of disaccharides containing galactose and xylose. Modification of the technique gave sulphated oligomers com-prising galactose and arabinose, a large proportion (60%) consisting of a mixture of sulphated pentasaccharides (galactose : arabinose 1:4). By alkali treatment. By alkali treatment, ionophoresis, methylation and periodate oxidation it was possible to deduce the overall structure of these oligomers. 4. Partial desulphation with methanolio hydrogen chloride gave a 63% recovery of polysaccharide in which the sulphate content was halved. The recovered polysaccharide from which a considerable proportion of the galactose had been removed was completely methylated and the derived methylated sugars characterised. The major structural feature is linked arabinose, with xylose constituting the major end group The three methods of attack on this polysaccharide have provided complimentary results and from them the highly branched nature of the polymer is confirmed f the various linkages between sugars elucidated; and, for the first time the presence of a repeating structure, comprising blocks of at least eight linked arabinose units, some sulphated at C-3 linked together by single galactose residues is established as a major feature of the polysaccharide. Furthermore sequential Smith's degradation provides a simple technique for use in chemotaxonomlc studies of this type of polysaccharide.