A water soluble β-glucan of an edible mushroom Termitomyces heimii: Structural and biological investigation

A water soluble β-glucan (PS-I) with an average molecular weight ∼1.48 × 105 Da was isolated from the alkaline extract of an edible mushroom Termitomyces heimii. PS-I contained (1 → 3)-, (1 → 6)-, (1 → 3, 6)-linked and terminal β-d-glucopyranosyl moieties in a ratio of nearly 2:1:1:1. Based on the total hydrolysis, methylation analysis, periodate oxidation, Smith degradation, partial hydrolysis and 1D/2D NMR experiments the structure of the PS-I was elucidated. On the basis of these experiments, the repeating unit of the polysaccharide was found to consist of a backbone chain of two (1 → 6)-β-d-glucopyranosyl residues, one of which was branched at O-3 position with the side chain consisting of two (1 → 3)-β-d-glucopyranosyl and a terminal β-d-glucopyranosyl residue. Cytotoxic effect of PS-I on human blood lymphocytes at varied concentrations was studied. Moreover, it also exhibited potent antioxidant activities by diminishing the ROS and NO in the nicotine stimulated lymphocytes up to 200 μg/ml.