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An alkali-soluble glucan from the cell walls of Saccharomyces cerevisiae NCYC1109 has been hydrolysed with a purified endo-(1 leads to 3)-beta-D-glucanase and an endo-(1 leads to 6)-beta-D-glucanase from Bacillus circulans WL-12. The products of enzyme action include various oligosaccharide and polysaccharide fractions which have been separated by gel filtration and characterized, giving new information on the fine structure of the glucan. The isolated cell walls have also been subjected to enzymic hydrolysis. The results suggest that part of the cell-wall mannan is held in place by a glucan component.

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.