663. The constitution of laminarin. Part III. The fine structure of insoluble laminarin

Abstract

ABSTRACT Soluble laminarin from Laminaria saccharina has been examined by methylation and periodate oxidation methods of analysis. An acid hydrolysate of the methylated polysaccharide contained 10% of 2,3,4,6-tetra-O-methyl glucose, 65% of 2, 4,6-tri-O-methyl glucose, ca. 1% of 2,3,4-tri-O-methyl glucose, 21% of di-O-methyl glucoses, and 3% of mono-O-methyl glucose. The average chain length is therefore 10, a value confirmed by measurement of the formic acid produced on periodate oxidation, and since the polysaccharide had a degree of polymerisation of 28, clear evidence of a small degree of branching is provided. The absence of a significant amount of 2,3,4-tri-O-methyl glucose shows that the 1,6-glucosidic linkages in laminarin are present as inter-chain linkages and not as inter-residue linkages. This conclusion is confirmed by the fact that the reaction sequence: periodate oxidation, borohydride reduction and mild acid hydrolysis (Smith degradation) does not cause fragmentation of soluble laminarin. These results are similar to those obtained previously with insoluble laminarin, with the exception that the latter has a much lower degree of branching. Possible metabolic routes leading to the enzymic synthesis of β-1,3-glucosidic linkages in laminarin-type polysaccharides are discussed.