Now, Glycogen phosphorase is that enzyme that initiates step one of Glycogen breakdown. So ultimately, we see that the signal, the primary messenger molecule that initiates Glycogen breakdown in the liver cells is in fact leukagon. Now, what about epinephrine? Epinephrine also actually plays an important role, but a smaller role in liver cells. Epinephrine binds to beta adrenergic receptors as well as alpha adrenergic receptors. When it binds to the beta adrenergic receptor it basically follows a similar pathway to the pathway outlined here.