## 3 Biosynthetic Pathways and Key Enzymes of Mushroom Polysaccharides
### Effects of Key Enzymes on PS Production and Monosaccharide Composition
: that there was no significant association of UGP activity with PS biosynthesis [10; 12; 70],  
Figure 1: Proposed/deduced/hypothesized biosynthetic pathways for mushroom PSs. 1. Glucokinase (GK); 2. Phosphoglucose isomerase (PGI); 3. Fructose-1,6-biphosphatase (FBPase); 4. Phosphofructokinase (FPK); 5. Phosphomannose isomerase (PMI); 6. Phosphomannose mutase (PMM); 7. GDP-Man pyrophosphorylase (GMP); 8. GDP-Man dehydratase (GMD); 9. GDP-4-keto-6-deoxyymnanose epimerase/reductase (GMER); 10. Phosphoglucose mutase (PGM); 11. dTDP-glucose pyrophosphorylase (dTDP-GPP); 12 and 13. dTDP-Rha synthase (dTRS); 14. UDP-Glc pyrophosphorylase (UGP); 15. UDP-Gal-4-epimerase (UGE); 16. UDP-Glc dehydrogenase (UGDG). 17. UDP-glucuron decarboxylase/UDP-Xyl synthase (UXS); 18. UDP-Xyl-4-epimerase (UXE). which may be attributed to the different strains and methods. Therefore, the exact reason still requires further research. Enzyme activities of glucokinase (GK) [16], UDPG-dehydrogenase (UGDG) [11], and dTDP-Glc pyrophosphorylase (dTDP-GPP) [10; 70] have also been investigated. However, these studies showed no notable association between PS biosynthesis and activities of these enzymes. Relationships between the monosaccharide composition of PS and the activity of related enzymes were recently studied using a correlation coefficient (\(R^{2}\)) based on data obtained under various culture and carbon source conditions [15; 16]. Changes in PGM, PGI, and phosphomannose isomerase (PMI) activities were strongly correlated with Gal and Man mole percentages in \(G\). _Incidum_ EPS, based on \(R^{2}\) values obtained under various culture temperatures and initial pH values [15]. In contrast, under various carbon source conditions, PGI and PMI activities were correlated only with Man mole percentage, and PGM activity was correlated only with Gal mole percentage (Figure 2) [16]. GDP-Man pyrophosphorylase (GMP) activity, whose \(R^{2}\) with mole percentages of all monosaccharides under various culture conditions was low (<0.5), showed a stronger correlation with Man mole percentage under carbon source conditions. Taken together, results of these studies indicate that PGM, PGI, and PMI regulate the mole percentages of Gal and Man in EPS under various culture and carbon source conditions, whereas GMP regulates the mole percentage of Man only in response to carbon source. Key enzymes regulating monosaccharide synthetic pathways in \(G\). _Incidum_ EPS can thus be divided into two groups, based on responses to culture conditions and culture medium. Mole percentages of other monosaccharides (Glc, Ara, Fuc) and activities of other tested enzymes under the various conditions showed no significant correlations (\(R^{2}\) < 0.5) [16]. Figure 2: Correlations (\(R^{2}\)) between activities of exopolysaccharidearchide (EPS) synthesis enzymes and monosaccharide mole percentages under various carbon source conditions. **(A)** Phosphoglucose isomerase (PGI) and Man; **(B)** Phosphomannose isomerase (PMI) and Man; **(C)** GDP-Man pyrophosphorylase (GMP) and Man; **(D)** Phosphoglucose mutase (PGM) and Gal.