Interactions

The activity of glycogen phosphorylase is influenced by:

• hormones:
  • adrenaline:
    • binds to plasma membrane alpha-adrenergic receptors
    • increase the cellular calcium concentration that increases the activity of phosphorylase kinase
  • insulin:
  • on binding with its plasma membrane receptor, it activates several secondary messenger systems
    • cAMP concentration falls with less activation of protein kinase
  • glucagon:
  • on binding with plasma membrane receptor, particularly in liver, adenylate cyclase is stimulated
    • cAMP concentration rises with increasing activation of protein kinase
      
      
• intrinsic agents:
  • calcium:
    • important in muscle
    • increased concentration of calcium increases the activity of phosphorylase kinase a
  • energy state of cell: a low ratio of ATP/AMP results in increasing activation of phosphorylase b to a
• glucose-6-phosphate: an increased level of this product of glycogen phosphorylase feedsback to inhibit the activity of the enzyme

The activity of glycogen phosphorylase is intimately related to glycogen synthase; glycogen synthase catalyzes the reverse reaction during glycogenesis. The interaction between both enzymes is considered in the submenu.