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An alkali-soluble glucan was obtained from the cell walls of Saccharomyces cerevisiae NCYC1109 and baker's yeast by extraction with cold, dilute sodium hydroxide under nitrogen. The glucan, which represented approximately 20% of purified glucan was homogeneous and was shown to be free from contamination by other cell-wall polysaccharides by ultracentrifuging, gel filtration and electrophoresis. In addition to glucose, the glucan contained traces of mannose and nitrogen, but no hexosamine. Structural analyses revealed the presence of 80-85% (1 leads to 3)-beta-D linkages, 8-12% (1 leads to 6)-beta-D linkages and 3-4% branched residues linked through C-1, C-3 and C-6. The molecular weight of the glucan was estimated to be about 250000. Electron-microscopic examination of the cell walls after alkali extraction showed that an amorphous surface layer had been removed revealing numerous bud scar structures.

Yeast glucan as normally prepared by various treatments of yeast (Saccharomyces cerevisiae) cell walls to remove mannan and glycogen is still heterogeneous. The major component (about 85%) is a branched beta-(1-->3)-glucan of high molecular weight (about 240000) containing 3% of beta-(1-->6)-glucosidic interchain linkages. The minor component is a branched beta-(1-->6)-glucan. A comparison of our results with those of other workers suggests that different glucan preparations may differ in the degree of heterogeneity and that the major beta-(1-->3)-glucan component may vary considerably in degree of branching.

1. Polytoma uvella, when grown in an acetate-containing medium, synthesizes a starch-type polysaccharide. 2. The starch differs from normal plant starches in having a lower iodine affinity, and in being relatively insoluble; this latter property makes fractionation difficult. 3. The starch contains about 16% of amylose, and on fractionation yields a branched amylopectin component that is similar in structure to a typical plant starch amylopectin.

By selective enzymolysis, or chemical fractionation, a minor polysaccharide component has been isolated from yeast (Saccharomyces cerevisiae) glucan. This minor component has a degree of polymerization of about 130-140, a highly branched structure, and a high proportion of beta-(1-->6)-glucosidic linkages. The molecules also contain a smaller proportion of beta-(1-->3)-glucosidic linkages that serve mainly as interchain linkages, but some may also be inter-residue linkages.