And the enzyme that basically plays a key role in this process is known as protein phosphatase One or simply PP One. So what happens when our cells need to regenerate glycogen supplies? Well, an enzyme called protein phosphatase One, PP One, stimulates glycogenesis, the building of glycogen from glucose and turns off glycogen breakdown. Now, how does it actually achieve this? Well, protein phosphatase One basically activates this molecule back to this molecule. Remember, a phosphatase is something that defosphorylates a target enzyme and PP One defosphorylates the glycogen synthase back to glycogen synthase A and that activates this molecule.