Structure and chain conformation of water-soluble heteropolysaccharides from Ganoderma lucidum

Five water-soluble heteropolysaccharides designated GL-I to GL-V, were isolated from the cultured fruit body of Ganoderma lucidum. Using a range of techniques the samples are shown to be heteropolysaccharides, mainly composed of glucose, galactose, mannose, arabinose with the relatively low weight-average molecular weights of 6.1 × 104 to 18.4 × 104. The amount of uronic acid present is low. As successive isolations proceed to give GL-I to GL-V, the content of glucan increased, the content of galactan and mannan decreased, and the branching decreased from high to near linear. GL-I is most branched of the heteropolysaccharides with a 27.0% degree of branching, whereas GL-V is mainly a linear glucan. Due to their branched chains samples GL-I to GL-III are in a compact coil conformation in 0.9% NaCl at 25 °C, whereas GL-V has a slightly flexible chain. Atomic force microscopy images confirmed the spherical shape of samples GL-I to GL-III in water.