Glycogen Phosphorylase Combined Control by Allosteric Effectors and Phosphorylation

Glycogen Phosphorylase Combined Control by Allosteric Effectors and Phosphorylation 

I Glycogen phosphorylase catalyzes the removal of a 1 terminal glucose residue from glycogen. (The struc- 

This is the first step in the metabolic breakdown of glycogen to pyruvate. 

In the early 1940s, Carl Cori and Gerty Radnitz Cori discovered that phosphorylase exists in two forms, a and b, 

The rate of the reaction catalyzed by glycogen phosphorylase, as a function of the concentration of its main allosteric activator, AMR The curves shown in color were obtained in the presence of ATR Phosphorylase b (lower two curves) is almost completely inactive in the absence of AMR Its activity is half maximal at an AMP concentration of about 40 yuM. ATP greatly increases the concentration of AMP required for activity. Phosphorylase a (upper two curves) has about 80% of its maximal activity in the absence of AMP and reaches full activity at very low AMP concentrations it also is relatively insensitive to inhibition by ATP. 

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Allosteric Enzymes Typically Exhibit a Sigmoidal Dependence on Substrate Concentration The Symmetry Model Provides a Useful Framework for Relating Conformational Transitions to Allosteric Activation or Inhibition Phosphofructokinase Allosteric Control of Glycolysis Is Consistent with the Symmetry Model Aspartate Carbamoyl Transferase Allosteric Control of Pyrimidine Biosynthesis Glycogen Phosphorylase Combined Control by Allosteric Effectors and Phosphorylation... 

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