## 2 Monosaccharide Composition, Combinations, and Bioactivities of Mushroom Polysaccharides
### Bioactivities of Mushroom PSs with Differing Monosaccharide Composition/Combinations  
PSs are highly complex molecules, and detailed characterization of specific glycosidic linkages, degree of branching, monosaccharide composition, molecular weight, and chain conformation is essential for elucidating structure--biological activity relationships. Increasing attention has been paid during the past decade to the relationship between PS composition and biological activity. PSs with differing monosaccharide compositions differ in their biological activities and therapeutic effects. In some cases, PSs with high content/ratio monosaccharide, such as Man, Rha, and Fuc, appear to be responsible for the bioactivity. For examples, Man-rich exopolysaccharidearchide (EPS) from _Tremella mesenterica_[47] and Rha-rich EPS from _Lactobacillus rhamnosus_[48] stimulate the immune system through receptors located on macrophage. l-Fuc-enriched EPS is used as a skin moisturizing agent in the cosmetic industry because l-Fuc displays anticancer and anti-inflammatory activities [49]. PSs containing high levels of uronic acid display significant antioxidant activity, and may be attributed to the presence of the functional group -COOH [7]. Functional groups that act as efficient electron or hydrogen donors are associated to the antioxidant activity of certain PSs [50]. Man is a typical component of many bioactive PSs. Most of these PSs also confer virulence against pathogenic species. Human cells are also able to recognize such carbohydrates through Man receptors, thus stimulating cytokine production [51; 52]. The high molar proportion of Man in _Inonotus obliquus_ PSs may enhance antioxidant activity [53; 54]. [PERSON] et al. reported an anti-cancer effect by endo-PS fractions from cultivated mycelia of _I. obliquus_ with Man as the major component [55]. [PERSON] et al. showed that the Man component of _Tremella mesenterica_ EPS stimulated nitric oxide (NO) and cytokine (IL-6 and TNF-\(\alpha\)) production in RAW 264.7 macrophage cells [47]. The major pharmacologically-active substance in _Tremella_ is the PS glucuronoxylomanan, composed primarily of Man [56]. Biological activity of certain mushroom PSs is related to content of other monosaccharides such as rhamn (Table 3). Rha as a major monosaccharide component may enhance antioxidant capacity, and play a role in radical-scavenging ability [34; 57]. Biological activities displayed by active components in mushroom PSs are summarized in Table 3.  
Many researchers have used a model, based on relationships between monosaccharide composition ratios and biological activities, to provide theoretical support for applications of PS from natural products. [PERSON] et al. observed a strong correlation between monosaccharide composition and ferrous ion chelating ability, and showed that Rha level in PSs was the dominant component in modulation of the chelating response variable [6]. In another study, [PERSON] et al. used statistical methods (multiple linear regression analysis, principal component analysis (PCA), factor analysis) to examine relationships between monosaccharide composition ratios and macrophage stimulatory activities of regionally different strains of _Lentinua edodes_[62]. Ara, Xyl, Man, and Gal were most strongly related to macrophage stimulatory activities. When additional PCA and factor analysis methods were applied to the same monosaccharide composition ratio data, Ara, Xyl, Man, and Gal compositions were again found to be the most important. Glc, although present as a major monosaccharide component in all strains and presumably forming the backbone of PS structures, was not a major determinant factor for structural characteristics or _in vitro_ macrophage stimulatory activities [62]. [PERSON] et al. used multiple linear regression