Our liver cells and skeleton muscle cells are responsible for glycogen breakdown. And what that basically means is they have to be able to regulate the process of the breakdown of glycogen. Now, how exactly do these two different types of cells regulate glycogen breakdown? Well, one point of regulation is the enzyme glycogen phosphorlase. And remember, as we discussed us in the previous lecture, this is the enzyme that is responsible for actually catalyzing step one of glycogen breakdown. So glycogen phosphorylase basically cleaves the alpha one four glycocitic bond and releases a glucose one phosphate from the glycogen polymer molecule.