GlcNAc GIcNAc

A second GIcNAc residue is added to the first, again using UDP-GlcNAc as the donor. 

An important additional pathway is indicated in reactions I and II of Figure 47-9. This involves enzymes destined for lysosomes. Such enzymes are targeted to the lysosomes by a specific chemical marker. In reaction I, a residue of GIcNAc-1-P is added to carbon 6 of one or more specific Man residues of these enzymes. The reaction is catalyzed by a GIcNAc phosphotransferase, which uses UDP-GlcNAc as the donor and generates UMP as the other product ... 

One of the minor by products of the isolation procedure of the disaccharide from lysozyme digests of bacterial cell walls was the tetrasaccharide /i-GIcNAc-G 4)-/i-MurNAc-G 4)-/)-GlcNAc-(l 4)-MurNAc. This structure is readily cleaved by lysozyme, and has proved to be extremely useful in other laboratories for the study of the mechanism of action of the enzyme. 

Figure 9.11 Structure of an oligosaccharide unit of human transferrin. The linkage between the oligosaccharide and polypeptide chains is of the N-asparaginyl type. Dotted arrows indicate positions in which one sometimes finds NeuNAc-Gal-GlcNAc units. Gal is galactose, GIcNAc is N-acetylglucosamine, NeuNAc is N-acetylneuraminic acid (sialic acid), and Man is mannose. (Reproduced with permission from Bezkorovainy A. Biochemistry of Nonheme Iron. New York Plenum Press, 1980, p. 175.)...

GIcNAc Analogues as Tools to Study 0-GlcNAc Protein Modification... 

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