The structure and organization of the polysaccharides of yeast
The polysaccharides present in the yeast cell are best considered in relation to the total organization of the cell both as regards their function and. their synthesis. Three polysaccharides may be extracted from the cells as distinc:t entities and these represent the storage material, glycogen, and the strue1:ural components, glucan and mannan. The three polysaccharides may be extracted from the yeast by cytolysing the cells with hot 3 per cent sodium hydroxide solution 1 which brings most of the mannan and a little of the glycogen into the solution and leaves an insoluble residue ofglucan membranes enclosing the bulk ofthe glycogen2, 3. The glycogen may then be dissolved from this latter material by hot 0·5 N aceric acid3, 4 and precipitated and purified by addition of alcohol. The mannan is precipitated from the alkaline solution as the copper complex which is decomposed by acid alcohol and the crude polysaccharide is purified by dissohring it in water and reprecipitating it with alcohol5• Alterna.tively, the cell wall of the yeast may be isolated free from the cell contents by breaking the cell with fine glass beads in a sonic vibratory mill and the resultant suspension fractionated by differential centrifugation2. U nder these conditions the cell wall may be analysed free from the glycogen which is ~.haken out of the cell envelope and appears in the supernatant with the other cell contents. The mannan and glucan may then be separated by gentle chemical extraction of the mannan from the wall fraction and the glycogen isolated from the cell contents without the use of strong alkali2 •