Phosphorylase cuts glucose units off a glycogen chain as glucose 1-phosphate, which becomes glucose 6-phosphate
Route: Glycogen chain end plus one glucose (maltotriose stand-in) → Glucose 1-phosphate + Glycogen chain end (maltose stand-in) → Glucose 6-phosphate
Glycogen phosphorylase breaks the alpha-1,4 bond at the end of a chain with phosphate and releases glucose 1-phosphate. No ATP is needed, because the released glucose is already phosphorylated. The cut is a phosphorolysis, and the enzyme uses the coenzyme pyridoxal phosphate. The drawing shows the maltotriose stand-in losing one glucose unit and becoming the maltose stand-in. A real chain is far longer, and the enzyme works along it one unit at a time. Phosphorylase stops four units from a branch point. A debranching enzyme (a transferase and an alpha-1,6-glucosidase in one protein) then moves three units to another branch and cuts the last unit at the branch point, which releases free glucose. Phosphoglucomutase converts glucose 1-phosphate into glucose 6-phosphate, which enters glycolysis or the pentose phosphate pathway. The liver can also remove the phosphate with glucose 6-phosphatase, the last enzyme of gluconeogenesis, and release glucose into the blood. Muscle has no glucose 6-phosphatase. The structure shown is the muscle form of phosphorylase.
Practice this pathway All pathways
| Step | Enzyme | EC | In | Out |
|---|---|---|---|---|
| 1 | Glycogen phosphorylase | 2.4.1.1 | Pᵢ | |
| 2 | 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).