The water-soluble polysaccharides of Cladophora rupestris. Part IV. Autohydrolysis, methylation of the partly desulphated material, and correlation with the results from Smith degradation
Attempted fractionation, on a Sagavac column, by gel electrophoresis, and by ultrafiltration, have all confirmed that the water-soluble mucilage from Cladophora rupestris is a polydisperse heteropolysaccharide. Autohydrolysis gave a number of disaccharides containing galactose and arabinose, galactose and xylose, sulphated trisaccharides containing two galactose and one arabinose residue, and sulphated pentasaccharides containing arabinose to galactose in the molar ratio of 4 : 1. Evidence is advanced for the structure of the majority of these oligosaccharides. Complete methylation of the partly desulphated partly degraded polysaccharide has confirmed the presence of many of the linkages tentatively deduced by us from methylation of the initial polysaccharide, and also shown that a major structural feature of the inner part of the molecule consists of at least eight 1,4-linked arabinose units joined together by a single 1,3- or 1,3,6-linked galactose residue, and that xylose is part of the same macromolecule. From an examination on a Sagavac column of the three degraded polymers isolated after three sequential Smith degradations it is concluded that the first degradation reduced the average molecular size down to about 5% of that of the initial polysaccharide. The two subsequent degradations caused comparatively little change in the average molecular size. These findings and further deductions concerning the extent of oxidation of the different sugars at each Smith degradation are discussed in relation to the present hydrolysis and methylation results.