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Literature summary for 2.4.1.1 extracted from

  • Agius, L.
    Role of glycogen phosphorylase in liver glycogen metabolism (2015), Mol. Aspects Med., 46, 34-45.
    View publication on PubMed
Search for more literature for 2.4.1.1

Activating Compound

Activating Compound Comment Organism Structure
AMP AMP causes little activation of liver glycogen phosphorylase b except in conditions of high concentrations of sulfate and other anions. Liver phosphorylase binds AMP with lower affinity than the muscle isoform and while AMP increases its affinity for glucose 1-phosphate this effect is smaller than for the muscle isoform Homo sapiens
Insulin Insulin promotes conversion of GPa to GPb via protein kinase B activation Homo sapiens
additional information the muscle isoform of phosphorylase is activated by phosphorylation (GPb to GPa conversion) Homo sapiens

Crystallization (Commentary)

Crystallization (Comment) Organism
crystallization and structure determination of liver and muscle enzymes Homo sapiens

Inhibitors

Inhibitors Comment Organism Structure
Caffeine inhibition of the liver enzyme, counteracted by AMP Homo sapiens
D-glucose liver GPa is inhibited by glucose Homo sapiens
glucose 6-phosphate inhibits the phosphorylated and unphosphorylated enzyme forms. Binding of glucose 6-phosphate to the muscle isozyme is competitive with binding of AMP, but it also stabilizes a conformation that is more tense than the native T-state enzyme. Inhibition of muscle GPa enzyme activity by G6P is additive with inhibition by glucose Homo sapiens
riboflavin inhibition of the liver enzyme, counteracted by AMP Homo sapiens
uric acid inhibition of the liver enzyme, counteracted by AMP Homo sapiens

Organism

Organism UniProt Comment Textmining
Homo sapiens P06737
-
-

Posttranslational Modification

Posttranslational Modification Comment Organism
phosphoprotein the muscle isoform of phosphorylase is activated by phosphorylation (GPb to GPa conversion) Homo sapiens

Source Tissue

Source Tissue Comment Organism Textmining
liver
-
 Homo sapiens
-
skeletal muscle
-
 Homo sapiens
-

Synonyms

Synonyms Comment Organism
GPA
-
 Homo sapiens
GPb
-
 Homo sapiens

General Information

General Information Comment Organism
metabolism glycogen degradation and synthesis during the diurnal cycle are mediated by changes in the activities of phosphorylase and glycogen synthase. Phosphorylase is regulated by phosphorylation of Ser14. Only the phosphorylated form of liver phosphorylase (GPa) is catalytically active. Interconversion between GPa and GPb (unphosphorylated) is dependent on the activities of phosphorylase kinase and of phosphorylase phosphatase. The latter comprises protein phosphatase-1 in conjunction with a glycogen-targeting protein (G-subunit) of the PPP1R3 family. Both GPa and phosphorylated glycogen synthase serve as substrates for the catalytic subunit of protein phosphatase-1 in association with G-subunits Homo sapiens
additional information despite a high degree of conservation of residues between liver and muscle isoforms in the ligand binding residues at the catalytic and allosteric sites, the kinetic properties of liver phosphorylase differ from the muscle isoform Homo sapiens
physiological function all three isoforms of phosphorylase are regulated allosterically by binding of several metabolite effectors and by reversible phosphorylation of Ser14. The phosphorylase exists as an equilibrium of conformational states, represented by the active conformation (relaxed or R-state) and an inactive conformation (Tense or T-state). The R-state has a high affinity for substrates and certain allosteric effectors such as AMP. The T-state has a low affinity for the substrates, glycogen and phosphate. Although GPb is essentially catalytically inactive in the liver, the various allosteric effectors that stabilize the T-state or R-state determine the interconversion of GPa and GPb through altered accessibility of the phospho residue to the catalytic subunit of protein phosphatase-1, PP1c. D-Glucose is the main physiological ligand that promotes conversion of GPa to GPb in liver, conversion of GPa to GPb by PP1c bound to a G-subunit, overview Homo sapiens