Structural features and immunological activity of a polysaccharide from Dioscorea opposita Thunb roots

A new polysaccharide (YP-1) from a variety of Chinese yam, Dioscorea opposita Thunb, having health benefits was extracted by water and further successively purified through DEAE-Cellulose A52 and Sephadex G-100 columns. YP-1 contained glucose, mannose and galactose in the molar ratio of 1:0.37:0.11. Its molecular weight was determined to be 42 kDa by high-performance gel-permeation chromatography. Structure features of the purified polysaccharide were investigated by a combination of chemical and instrumental analysis, such as methylation analysis, Smith degradation, GC-MS, 13C and 1H NMR and FT-IR. The results indicated that the polysaccharide has a backbone of (1→3)-linked α-d-glucopyranosyl residues, which occasionally branches at O-6. The branches were mainly composed of (1→2)-linked α-d-mannopyranosyl residues, and terminated with β-d-galactopyranosyl residues. Preliminary tests in vitro revealed that YP-1 could stimulate ConA-induced T lymphocyte proliferation and its branches are extremely important for the expression of the enhancement of the immunological activity.