Chain conformation and bioactivity of water-soluble polysaccharide extracted from Rhizoma Panacis Japonici.

A water-soluble alpha-(1-->4)-D-glucan heteropolysaccharide with 37% degree of branch extracted by base from Rhizoma Panacis Japonici, coded as RPS3, was fractionated into six fractions by the method of nonsolvent addition. Their weight-average molecular mass (M(w)), polydispersity index (M(w)/M(n)), and radius of gyration (s(2)(z) (1/2)) were determined with laser light scattering (LLS) and size exclusion chromatography combined with LLS. The structure of the fraction was determined by methylation analyses and (13)C NMR. The dependences of intrinsic viscosity ([eta]) and s(2)(z) (1/2) on M(w) were established as [eta] = 0.71 M(w) (0.27 +/- 0.01) (cm(3)/g) and s(2)(z) (1/2) = 1.53 M(w) (0.27 +/- 0.02) (nm) in the M(w) range from 5.62 x 10(4) to 3.05 x 10(6) (g/mol) for RPS3 in 0.15M NaCl aqueous solution at 25 degrees C. On the basis of the current theory of the polymer solution, the fractal dimension (d(f)), unperturbed chain dimension (A), and characteristic ratio (C(infinity)) were calculated to be 3.0, 1.48 A, and 15.1, respectively. The results revealed that the RPS3 chains existed as spherical conformation in the aqueous solution. Transmission electron microscope further provided the evidence of the sphere shape of the RPS3 and its fractionated molecules in water. In vitro cytotoxicity assay indicated that the fractions could inhibit the tumor cells and showed no harm to normal cells at low dose. The bioactivity was relative with molecular mass of the samples.