regulation
Last reviewed 01/2018
Glycogen phosphorylase is the key enzyme in glycogenolysis as it is rate-limiting; the remaining enzymes in the pathway are near equilibrium and non-saturated. Consequently, agents which alter glycogen phosphorylase activity alter the rate of glycogenolysis.
The agents are best considered in terms of site as there is slight variation:
- the liver, where glycogenolysis is tailored to plasma blood glucose concentration:
- hormones:
- glucagon and adrenaline increase glycogenolysis
- insulin decreases glycogenolysis
- local factors:
- the intracellular glucose concentration feedsback to inhibit glycogen phosphorylase, so providing fine-control over glycogenolysis
- calcium increases glycogenolysis
- low energy state within the cell increases glycogenolysis
- in skeletal muscle:
- hormones: as above, but glucagon has minimal effect
- local factors: as above, but calcium release during muscular contraction has a more significant role in rapid activation of glycogen phosphorylase