Structural studies of a polysaccharide isolated from an edible mushroom, Astraeus hygrometricus

The polysaccharide (PS) isolated from the hot aqueous extract of the mushro om, Astraeus hygrometricus contains D-galactose, D-glucose and D-galacturon ic acid in a mole ratio of about 1.9:0.9:1.0. From the periodate oxidation and methylation studies of PS, the linkages among the constituent sugar res idues are identified as, D-Gal(p) (1,6)-linked, D-Gal(p) (1,2,6)-linked, D- Glc(p) (1,3)-linked and D-Gal(p) UA is glycosidically linked. The linkages have been confirmed by partial acid hydrolysis studies of PS followed by GL C analysis. The anomeric configurations of the constituent sugar residues h ave been determined by chromium trioxide oxidation of the acetylated PS fol lowed by GLC analysis of the surviving sugar residues and it has been found that galactose and galacturonic acid have beta -configuration and glucose has alpha -configuration. Based on the above studies, the structure of the repeating unit of PS has been assigned as: [GRAPHICS]