Molecular mass and chain conformation of carboxymethylated derivatives of beta-glucan from sclerotia of Pleurotus tuber-regium.

Abstract

Seven water-insoluble (1 --> 3)-beta-D-glucan fractions TM8-1 to TM8-7 with weight-average molecular mass M(w) ranged from 2.22 to 77.4 x 10(4) obtained from the sclerotia of Pleurotus tuber-regium were carboxymethylated to produce the water-soluble fractions CTM8-1 to CTM8-7 with M(w) ranged from 3.87 to 87.8 x 10(4). The degree of substitution (DS) of CTM8 fractions was analyzed by ir and elemental analysis (EA) to be 0.3-0.68. The M(w) and the intrinsic viscosity [eta] of the CTM8 fractions were measured by size-exclusion chromatography combined with multiangle laser light scattering (SEC-MALLS), MALLS, and viscometry in phosphate buffer solution (PBS) at 37 degrees C. The dependencies of [eta] and radius of gyration <s(2)>(z) (1/2) on M(w) for the CTM8 samples were found to be [eta] = (8.82 +/- 0.03) x 10(-3) M(w)(0.78 +/- 0.04) (cm(3) g(-1)) and <s(2)>(z) (1/2) = (3.09 +/- 0.05) x 10(-3) M(w)(0.75 +/- 0.06) (nm) in the M(w) range from 3.87 x 10(4) to 53.2 x 10(4). Based on current theories for wormlike chain model, the conformational parameters of the CTM8 were obtained to be 790 (nm(-1)) for M(L), 9.6 (nm) for q, which were higher than those of the native TM8 fractions, suggesting a more extended flexible chain of CTM8 in PBS. On the whole, the CTM8 fractions showed higher antitumor activity than their corresponding TM8 fractions. In view of data from molecular parameters and bioactivity, the antitumor activity of the CTM8 fractions may be correlated to its water solubility and relatively extended chain.