Galactose to glucose 6-phosphate in four steps, so that it can enter glycolysis
Route: Galactose → Galactose 1-phosphate → Glucose 1-phosphate + UDP-galactose → Glucose 6-phosphate → UDP-galactose + UDP-Glc
Galactose, a sugar abundant in dairy products, is turned into a glucose compound in four steps. Galactokinase phosphorylates galactose with ATP and gives galactose 1-phosphate. Galactose 1-phosphate uridyl transferase takes the uridyl group of UDP-glucose and puts it on galactose 1-phosphate. This releases glucose 1-phosphate and makes UDP-galactose. UDP-galactose 4-epimerase inverts the hydroxyl group on carbon 4 of UDP-galactose, which gives back UDP-glucose, so UDP-glucose is not used up. The board shows the epimerase last; in the cell it runs alongside the other steps and supplies UDP-glucose to the transferase. Finally phosphoglucomutase moves the phosphate of glucose 1-phosphate from carbon 1 to carbon 6, and glucose 6-phosphate enters glycolysis. The sum is galactose + ATP to glucose 1-phosphate + ADP, with UDP-glucose as a carrier that is regenerated. The reaction of the epimerase also runs in the other direction, which makes UDP-galactose when the diet does not supply enough galactose for glycoproteins and complex polysaccharides. Classic galactosemia is an inherited deficiency of the transferase. Galactose and galactose 1-phosphate then build up, and infants fail to thrive and develop liver disease and cataracts. Cutting galactose and lactose from the diet prevents the liver disease and the cataracts, although most patients still have problems with the nervous system.
Practice this pathway All pathways
| Step | Enzyme | EC | In | Out |
|---|---|---|---|---|
| 1 | Galactokinase | 2.7.1.6 | ATP | ADP |
| 2 | Galactose-1-phosphate uridylyltransferase | 2.7.7.12 | UDP-Glc | |
| 3 | Phosphoglucomutase | 5.4.2.2 |
Build any of these from its atoms.
Enzyme names and EC numbers are those used on the interactive board. Checked against sources: see the claim table in the repository (tools/pathway_data/checks).