Chemical Structure and Molecular Weights of α-(1→3)-D-Glucan from Lentinus edodes

α-Glucan (L-FV-II) and β-glucan (L-FV-I) were isolated from fruiting bodies of Lentinus edodes by extraction with 5% NaOH/0.05% NaBH4, then precipitation with 1 M acetic acid. The analysis results of Smith degradation, high-performance liquid chromatography (HPLC), infrared spectra (IR), (13)C NMR spectra, and optical rotation indicated that L-FV-II is α-(1→3)-D-glucan with slight (1→6) branch linkages, and L-FV-I is β-(1→3)-D-glucan containing 10% protein, and with branches. The weight-average molecular weight, Mw, number-average molecular weight, Mn, radii of gyration, (1/2), and second virial coefficients, A2, of L-FV-II in aqueous 0.5 M urea/0.5 M NaOH (obtained from diluting its solution in 1.0 M urea/1.0 M NaOH) and 0.25 M LiCl in dimethylsulfoxide (DMSO/0.25 M LiCl) were measured by light scattering, membrane osmometry, and size exclusion chromatography (SEC). The values of Mw and Mn for L-FV-II in 0.5 M urea/0.5 M NaOH are 24.1×10(4) and 10.9×10(4), respectively, similar to those in DMSO/0.25 M LiCl. It was proved that strong intermolecular hydrogen bonds exist in L-FV-II, resulting in its water-insolubility, but there are not any aggregates or multiple-helix structure for L-FV-II in DMSO/0.25 M LiCl. The chain of α-(1→3)-D-glucan is more extended in DMSO/0.25 M LiCl than that in the aqueous solution.