Fig. 3
From: Fueling the fire: emerging role of the hexosamine biosynthetic pathway in cancer
Hexosamine extended and salvage pathways. The GlcNAc salvage pathway utilizes GlcNAc via NAGK (N-acetylglucosamine kinase) to feed directly into GlcNAc-1P and produce UDP-GlcNAc . UDP-GlcNAc and UDP-GalNAc can be interconverted using GALE (UDP-glucose 4-epimerase/UDP-galactose 4-epimerase). GALE also converts UDP-glucose that comes from a three-step conversion from glucose, making more UDP-GlcNAc and UDP-GalNAc, which are both used for glycosylation in the ER and Golgi. UDP-GlcNAc can make ManNAc-6P through GNE (UDP-GlcNAc 2-epimerase/ManNAc kinase) and produce CMP-sialic acid that is utilized by the Golgi for sialylated glycoconjugation. Fructose-6P also interconverts to ManNac-6P through MPI (mannose phosphate isomerase) to produce GDP-Man (GDP-mannose) and GDP-Fuc (GDP-fucose) that are then used for glycosylation