Abstract
Insoluble laminaran, a (1→3)-β- D-glucan from Laminaria hyperborea ( L. cloustoni), has been fractionated by differential solubility into soluble and insoluble fractions. These fractions were degraded with a purified exo-(1→3)-β- D-glucanase from Basidiomycete sp. QM806 giving, as primary hydrolysis products, D-glucose, gentiobiose, laminarabiose, and 1- O-β-laminarabiosylmannitol. Gentiobiose was obtained in only trace amounts from the insoluble fraction of laminaran, suggesting the absence of branching. Successive application of periodate oxidation, reduction, mild acid hydrolysis, and enzymic degradation indicated that the branch in the soluble fraction consists of a single β-(1→6)-linked D-glucosyl residue. The results indicate that “insoluble” laminaran is apparently an aggregate of three closely related polysaccharide species: a soluble, branched, reducing component (soluble laminarose); an insoluble, unbranched, reducing component (insoluble laminarose); and an unbranched, nonreducing component (laminaritol) that has a monosubstituted mannitol residue at the reducing terminal. Laminaritol was found to be about equally distributed between the soluble and insoluble fractions. The average d.p. of the laminaran components is 20–25 residues, as determined from the relative amounts of enzymic hydrolysis products and from periodate-oxidation data.
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