An antitumor, branched (1 → 3)-β- d-glucan from a water extract of fruiting bodies of Cryptoporus volvatus

Abstract

A water-soluble, (1 → 6) -branched (1 → 3)-β- d-glucan (H-3-B) was isolated from a hot-water extract of the fruiting bodies of the fungus, Cryptoporus volvatus (Basidiomycetes). Enzymatic analysis using exo-(1 → 3)-β- d-glucanase and methylation analysis indicated that this polysaccharide has a main chain composed of β-(1 → 3)-linked d-glucopyranosyl residues, and single, β-(1 → 6)-linked d-glucopyranosyl residues attached as side chains to, on average, every fourth sugar residue of the main chain. This structure was confirmed by 13CNMR spectra of the glucan in Me 2SO- d 6. The weight-average molecular weight ( M w) of H-3-B was determined to be 44.0 × 10 4 by gel permeation chromatography equipped with a low-angle laser-light-scattering photometer. The electron microscopic observations showed that H-3-B and its sonicated sample (S-H-3-B, M w = 13.7 × 10 4) can be described as linear worm-like chains. The mass per unit length for native and sonicated H-3- B was determined to be 1750 and 1780 g mol −1 nm −1, respectively, from the contour lengths obtained by electron microscopy and the molecular weights. These values are in good agreement with that expected for the triple stranded structure. A sample denatured in 0.1 M NaOH and subsequently renatured by neutralization showed a mixture of linear and cyclic structures, and larger aggregates with less well-defined morphology. The H-3-B and S-H-3-B had antitumor activity against the Sarcoma 180 tumor.