GPLase

Glycogen - Glycogen Catabolism

Allosteric enzyme cleaves Glycogen by acctacking GLC in the non reducing ends

Glycogen, Glucose

Fundamentals:

• Regulation by several allosteric affectors
• Reversible phosphorylation responsive to Hormones: Insulin, Epinephrine and Glucagon
• Different structure and regulation but similar funcitons in distinct tissues

LOC:

• Liver - required for the GLC maintenance
• Skeletal Muscle - required for glycogeon catabolism

Structures:

• Phosphorylate a - R state (relaxed) ACTIVE
• Phosphorylate a - T state (tense) INACTIVE
• Phosphorylate b - R state (relaxed) ACTIVE
• Phosphorylate b - T state (tense) INACTIVE

Isozymes:

• Liver - GLC sensitive, AMP insensitive
• Phosphorylase a is sensitive to GLC
  • Phosphorylase a is most responsive to R-T transition
    • GLC binding shifts equilibrium Phosphorylase a R into the T state
• Skeletal Muscle - dimer, Intracelllar Energy Charge
• R and T states (not discrete but usually active/inactive)
• Phosphorylase a equilibrium favors R
• Phosphorylase b equilibrium favors T

Regulation - hormones, AMP/ATP sensitive

• Phosphorylation of Serine 14 converts into Phosphorylase a
  • Phosphorylase Kinase
  • INC Epinephrine

Reguation - muscle contraction

• Active during INC AMP concentrations/LOW energy charge
  • AMP binds to nucelotide binding sites to stabilize actie site
• G-6P stabilizes the less active T state - Negative Feedback
• ATP acts negative allosteric effector
• Glucose 6-phosphatase absence = NO GLUCONEOGENESIS

Concepts:

• Allosteric Enyzmes - Enzymes
  • Relaxed and Tense states
• Negative Feedback
• Isozymes

Terminology:

• Non reducing: Carbohydrates