Abstract
Several β-D-glucans, appertaining to the same molecular species but having different degrees of branching, were isolated from water and alkali extracts of the fruiting body of Ganoderma lucidum (Reishi). The purified glucans that were mostly water-insoluble had a backbone of (1→3)-linked D-glucose residues, attached mainly with single D-glucosyl units at O-6 and also with a few short (1→4)-linked glucosyl units at O-2 positions. However, their degrees of branching appeared to differ in the range of d.b. 1/3-1/23, depending on the extracted glucan fractions. In addition to the β-glucans, the fruiting body contained water-soluble heteropolysaccharides, comprising D-glucose, D-galactose, D-mannose, L-(or o)-arabinose, D-xylose, and L-fucose.
A branched (1→3)-β-D-glucan was also isolated from the culture filtrate of G. lucidum grown in a glucose-yeast extract medium. The extracellular β-D-glucan was less soluble in water after purification, but soluble in dilute alkali. This glucan has essentially the same structure as that of hot-water extracted polysaccharide from the fruiting body. The repeating unit of the glucan contains a backbone chain of (1→3)-linked D-glucose residues, five out of sixteen D-glucose residues being substituted at O-6 positions with single D-glucosyl units and one D-glucose residue at O-2 positions probably with a cellobiose unit.
The hot-water extractable fruiting body glucan and the extracellular glucan of the culture of growing mycelium showed relatively high growth-inhibition activities against Sarcoma 180 solid tumor in mice, when administered by- successive intraperitoneal injections. When the moderately branched glucans were modified to D-glucan-polyols by periodate oxidation and borohydride reduction, they exhibited higher antitumor activities, confirming the previous conclusion that the attachment of polyol groups to the (1→3)-linked backbone significantly enhances its host-mediated antitumor effect.
