Steps of Covalent Modification of Glucagon

Step 1

When blood glucose levels are low, glucagon is secreted from the pancreas and travels through the blood til it arrives in the liver

Step 2

Once in the liver, the glucagon will bind the to cell receptor (R) to generate the signal

Step 3

When the signal is stimulated, the G protein and alpha separate from beta and gamma, as GDP replaces GTP on the unit, causes the separation and activates it

Step 4

The G protein and alpha travel through the transmembrane to reach the bound enzyme called adenylate cyclase (AC) and activate it

Step 5

Once active, AC hydrolyzes ATP to cAMP, releasing PPi

• PPi as there are 2 phosphates from ATP

Step 6

cAMP activates protein kinase (inactive) to protein kinase (active)

Step 7

Protein kinase (active) phosphorylates phosphorylase kinase (inactive) with ATP to phosphorylase kinase (+ P) (active) with ADP

Step 8

After it is active, phosphorylase kinase (active) phosphorylates phosphorylase (inactive) with ATP to phosphorylase (+P) (active) with ADP

What is happening with glycogen in this process?

Protein kinase deactivates glycogen synthase and activates phosphorylase to maintain glucose levels

What is happening with insulin in this process?

Insulin is released from the pancreas and activates a phosphatase in the cell, which dephosphorylates 3 enzymes:

1. phosphorylase (deactivated)

2. phosphorylase kinase (deactivated)

3. glycogen synthase (activated)