Electron microscopic study of purified polysaccharide components glucans and mannan of the cell walls in the yeast Saccharomyces cerevisiae

In this study electron-microscopic characteristics of platinum shadowed or negatively stained preparations of purified beta-(1----3)-D-glucan, beta-(1----6)-D-glucan, and mannan were examined. These polysaccharides were isolated from cell walls of the yeast Saccharomyces cerevisiae. While purified samples of beta-(1----6)-D-glucan and mannan proved to be amorphous in structure and homogenous in appearance, the purified beta-(1----3)-D-glucan, isolated and presented to us as alkali-insoluble yeast glucan A2, was not homogenous. It consisted of (i) fibrillar component, (ii) amorphous matrix, and (iii) chitin bud scars. The ultrastructure of beta-(1----3)-D-glucan present in the glucan A2 sample did not change after treatment with 0.5 M acetic acid at 75 degrees C for 2 hours. After treatment with 1 M NaOH for 3 days at 4 degrees C scar material was removed by centrifugation and after a subsequent acidification of supernatant with acetic acid both the microfibrillar and the amorphous components were still present. It was concluded that beta-(1----3)-D-glucan component consists of molecules probably differing in their physico-chemical properties such as D. P., the degree of branching, conformation, and that cannot be separated by the methods currently used for their isolation.