Phosphorylative allosteric transition

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... 

Studies on the reactivation of apoglycogen phosphorylase with a variety of analogs of pyridoxal phosphate have shown that the catalytic moiety is the 5 -phosphate group - only analogs with a reversibly protonatable dianion in this position have any activity In the nonactivated form of phosphorylase b, the phosphate is monoprotonated (-OPO3H ) when the enzyme has been activated, either allosterically or by phosphorylation (phosphorylase a), it is dianionic (-OPOa ). A glutamate residue in the active site acts as the proton acceptor or donor for this transition between the inactive and active forms of the cofactor. 

There are two major ways of control. One mechanism involves reversible covalent modifications, such as phosphorylation dephosphorylation, the other requires conformational transitions by binding an allosteric ligand or regulator protein. It follows an example of regulation of an enzyme, of which the activity is subject to control by both mechanisms, then we compare the regulation of an enzyme with regulation of components of cellular signalling pathways, of which many have no enzymic activity. 

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