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.