Describe how phosphorylation and dephosphorylation control the activity of glycogen phosphorylase

Glycogen Phosphorylase exists in two forms.A phosphoryl group is esterified to Serine 14 in the phosphorylated state of the enzyme, phosphorylase a. Phosphorylase b is the dephosphorylated form of the enzyme.

The enzymatically inactive T state and the enzymatically active R state are the two conformational states of glycogen phosphorylase.

The enzyme can take on either the enzymatically inactive T conformation (shown above) or the catalytically active R conformation (shown below). The effectors ATP, AMP, and G6P allosterically regulate the conformation of phosphorylase b, which is usually in the T state under physiological conditions.

The phosphorylated form of this enzyme, phosphorylase a, on the other hand, is insensitive to these effectors and is generally in the R state unless there is a lot of glucose available. Thus, glycogen phosphorylase’s enzymatic activity is substantially governed by its phosphorylation and dephosphorylation rates under normal physiological conditions.