Chemical structure and molecular weights of α-(1→3)-D-glucan from Lentinus edodes

alpha-Glucan (L-FV-II) and beta-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), C-13 NMR spectra, and optical rotation indicated that L-FV-II is alpha-(1-->3)-D-glucan with slight (1-->6) branch linkages, and L-FV-I is beta-(1-->3)-D-glucan containing 10% protein, and with branches. The weight-average molecular weight, M-w, number-average molecular weight, M-n, radii of gyration, [S-2](1/2) and second virial coefficients, A(2), 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 M-w and M-n for L-FV-II in 0.5 M urea/0.5 M NaOH are 24.1 x 10(4) and 10.9 x 104, 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 alpha-(1-->3)-D-glucan is more extended in DMSO/0.25 M LiCl than that in the aqueous solution.