| Fructose-6-phosphate (Fru-6-P)
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| Figure 25.9 Synthesis of amino sugars and sialic acid. Acetyl CoA, acetyl Coenzyme A; GlcN-6-P, glucosamine-6-phosphate; GlcNac-6P, N-acetylglucosamine-6-phosphate; GalNAc, acetylgalactosamine; HNAc, AcHN, acetamide group; PEP, phosphoenolpyruvate. |
| Fru-6-P is the common precursor of amino sugars, which are found in almost all glycoconjugates. Figure 25.9 shows the pathway of formation of GlcNAc, GalNAc, and sialic acid. The initial reaction involves transfer of an amino group
from glutamine to Fru-6-P, to form glucosamine-6-phosphate (GlcN-6-P). This is followed by transfer of acetate from acetyl-CoA to the amino group to form N-acetylglucosamine-6-phosphate (GlcNAc-6-P). GlcNAc-6-P is converted to its activated form, UDP-GlcNAc, by mutase and pyrophosphorylase reactions. In addition to its role as a GlcNAc donor, UDP-GlcNAc can also be epimerized to UDP-GalNAc.
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