N-acetyl-D-Glucosamine (GlcNAc) is a monosaccharide derivative of glucose. It is released by the action of O-GlcNAcase, in mammalian systems from proteins that have been post-translationally modified with O-GlcNAc. Levels of O-GlcNAcylation proteins from Alzheimer’s disease brain extracts are decreased as compared to that in controls, suggesting that release of GlcNAc may contribute to pathogenesis. In E. coli, GlcNAc induces the expression of multidrug exporter genes, indicating that this sugar can alter gene expression. GlcNAc is also the monomeric unit of chitin, which is found in fungi and many invertebrates, including crustaceans, insects, and nematodes. For this reason, chemicals that inhibit the incorporation of GlcNAc into chitin are cytotoxic to these organisms.