Studies on Fungal Polysaccharides. XXVII. Structural Examination of a Water-soluble, Antitumor Polysaccharide of Ganoderma lucidum

Abstract

A water-soluble, antitumor polysaccharide GL-1, [α]²⁰_D+26°(c=1, water), M.W. 40000, was isolated from the fruit bodies of Ganoderma lucidum (Rokkakushi, a kind of Reishi). GL-1 consists of glucose, xylose and arabinose in the molar ratio of 18.8 : 1.5 : 1.0. Structural examination was carried out by periodate oxidation, Smith degradation, methylation analysis, partial acid hydrolysis and α-amylase treatment. It is concluded that (1) GL-1 is a branched arabinoxyloglucan, (2) GL-1 contains backbone and side-chains involving D-glucopyranosyl (1→4)-α- and -β-, (1→6)-β- and (1→3)-β-linkages, (3) arabinose is present as a part of the non-reducing terminal residues, and (4) xylose may be present as a part of the side-chain. GL-1 strongly inhibited the growth of Sarcoma 180 solid-type tumor (inhibition ratio, 95.6-98.5%) when injected i. p. (20 mg/kg) for 10 days. Mild acid hydrolysis and α-amylase treatment of GL-1 had no effect on the antitumor activity. These results suggest that the essential structure for the antitumor activity of GL-1 is a branched glucan core (GL-3) involving (1→3)-β-, (1→4)-β-and (1→6)-β-linkages.