rate-limiting unreviewed

Glycogen phosphorylase

1 reactions · 1 pathways

Cofactors used

Pi PLP (B6) · B6 (Pyridoxine)

Clinical / pharmacological. McArdle disease (GSD V, muscle); Hers disease (GSD VI, liver)

What it does, reaction by reaction

1 reactions

Glycogenolysis (Glycogen Breakdown) Carbohydrate Metabolism · Cytosol + ER (liver)

step 1 Irreversible/directional rate-limiting

Glycogen(n) + Pi → glycogen(n−1) + glucose-1-phosphate

Converts Glycogen(n) Pi into Glycogen(n-1) Glucose-1-phosphate

› Notes

Glycogen phosphorylase uses inorganic phosphate (Pi) and the cofactor pyridoxal phosphate (PLP; vitamin B6) to phosphorolyze successive alpha(1→4) bonds at nonreducing ends. It stops four residues before an alpha(1→6) branch (a limit dextrin); this is the principal rate-limiting step and conserves the bond energy in glucose-1-phosphate rather than using ATP.

Showing all 1 reactions.

What accelerates and inhibits it

Regulation is pathway-specific, so each context is listed separately

1 entries

Glycogenolysis (Glycogen Breakdown)

Accelerated by

Phosphorylation by phosphorylase kinase; AMP in muscle; Ca2+ indirectly through calmodulin on phosphorylase kinase

Inhibited by

ATP and glucose-6-phosphate in muscle; glucose in liver promotes inactivation

Hormonal control

Glucagon activates liver phosphorylase through cAMP/protein kinase A; epinephrine activates liver and muscle pathways; insulin promotes dephosphorylation/inactivation

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