N-Acetyl-α-D-glucosamine (alpha-GlcNAc) is a major component of complex carbohydrates, that has been found in N- and O-glycans and glycolipids. Glycosaminoglycans and the glycosylphosphatidylinositol anchor of membrane-bound glycoproteins also contain GlcNAc moieties. GlcNAc is derived from the degradation of glycoconjugates by glycosidases and from nutritional sources. GlcNAc is converted into GlcNAc-6-phosphate by the N-acetylglucosamine kinase. GlcNAc-6-phosphate can enter a catabolic pathway that ultimately leads to the formation of fructose-6-phosphate, or it can enter an anabolic pathway leading to the formation of UDP-GlcNAc.