The hexosamine biosynthsis pathway (HBP) and protein O-GlcNAcylation. Enzymes are illustrated by orange circles. Blockers are written in red. Abbreviations: GFAT: l-glutamine-d-fructose 6-phosphate amidotransferase; UDP-GlcNAc: UDP-N-acetylglucosamine; OGT: uridine-diphospho-N-acetylglucosamine:polypeptide β-N-acetylglucosaminyltransferase; O-GlcNAcase: β-N-acetylglucosaminidase; DON: 6-diazo-5-oxo-norleucine; UDP-5SGlcNAc: uridine diphospho-5-thio-N-acetylglucosamine; TTO4: 2[(4-chlorophenyl)imino]tetrahydro-4-oxo-3-[2-tricyclo(3.3.1.13.7)dec-1-ylethel]; PUGNAc: O-(2-acetamido-2-deoxy-d-glucopyranosylidene)amino-N-phenylcarbamate; NAG:1,2-Dideoxy-2′-methyl-α-d-glucopyranoso-[2,1-d]-δ2′-thiazoline; NButGT:1,2-dideoxy-2′-propyl-α-d-glucopyranoso-[2,1-d]-δ2′-thiazoline. GFAT can be inhibited by glutamine analogue azaserine (O-diazoacetyl-L-serine) or DON. OGT can be inhibited by the uridine analogue alloxan, substrate analog of O-GlcNAc UDP-5SGlcNAc, or with TTO4, whereas O-GlcNAcylation of proteins can be rapidly increased by inhibiting O-GlcNAcase with PUGNAc, Thiamet G, NAG, or NButGT. Alloxan has also shown to have an inhibitory effect on O-GlcNAcase.