Figure 1.

Glycolysis and the HBP. This scheme shows important metabolic intermediates for these pathways. Intermediates shared between glycolysis and HBP are shown in black, HBP-only intermediates are shown in red, and glycolysis-only intermediates are shown in green. Glucose is initially metabolized to G6P in the first glycolytic step. F6P, the next glycolytic intermediate, can either enter the HBP or undergo further glycolysis to generate pyruvate. GFAT (shown in the red oval) is the rate-limiting enzyme in the HBP and uses glutamine to catalyze the conversion of F6P to glucosamine 6-phosphate. After a series of reactions, uridine diphosphate-β-GlcNAc (UDP-GlcNAc) is the end product of the HBP and serves as the donor for the enzyme OGT to perform O-GlcNAc protein post-translational modifications. The enzyme O-GlcNAcase (OGA) removes the GlcNAc moiety from proteins. UDP-GlcNAc can also be epimerized to UDP-GalNAc, metabolized to n-acetylmannosamine (ManNAc), or utilized in other glycoconjugation reactions. Pyruvate is the end product of glycolysis and can enter the citric acid cycle, be metabolized to lactate, or be excreted from the cell (cellular efflux) as pyruvate or lactate.