Glycogenolysis and Glycogenesis
glycogen metabolism, glycogenolysis

Glycogenolysis

  • Glycogen phosphorylase
    • Glycogenn → glycogenn-1 + G1P
    • Cleaves 1-4 linkage.
    • Can't touch residues near branch point.
    • Deficient in McArdle's disease (type V glycogen storage disease) in skeletal muscles. Symptoms: muscle exertion lead to painful cramps and muscle damage.
  • Glycogen debranching enzyme:
    • Transfers 1-4 linkage from near branch point somewhere else.
    • Cleaves 1-6 linkage for the last branch point residue to make glucose.
    • Deficient in Cori's disease (type III glycogen storage disease). Symptoms: milder version of type I.
  • Phosphoglucomutase:
    • Converts G1P → G6P.
  • Glucose-6-phosphatase:
    • Converts G6P → glucose.
    • Deficient in Von Gierke's disease (glycogen storage disease type I). Symptoms: hepatomegaly, ↑ liver glycogen that can't be broken down to glucose → severe hypoglycemia and ↑ blood lactate.
  • Lysosomal α-1,4-glucosidase:
    • Glycogen → glucose (in lysosome).
    • Deficient in Pompe's disease (type II glycogen storage disease). Symptoms: cardiomegaly, systemic findings leading to early death.

Glycogenesis

  • UDP-Glucose pyrophosphorylase: makes UDP-Glucose.
    • UDPG Pyrophosphorylase: G1P + UTP → UDPG + PPi
    • Pyrophosphatase: PPi → 2 Pi
    • Nucleoside diphosphate kinase: UDP + ATP → UTP + ADP.
  • Glycogen synthase: makes 1-4 glycogen linkage by adding UDP-Glucose.
    • Chain grows from 1→4
  • Glycogen branching enzyme: transfers a 1-4 to 1-6.
    • Also called amylo-(1,4→1,6)-transglycosylase.