So we said that in skeleton muscle cells we have the enzyme known as glycogen phosphorylase that can be regulated. And that in turn regulates the breakdown of glycogen. Now, in liver cells, things are slightly different, and that's because liver cells have a different function than of skeletal muscle cells. So in liver cells that's our goal is to actually regulate the concentration of glucose inside our blood. So our liver is responsible for regulating the concentration of glucose in the blood. And what that means is liver cells can actually mobilize glycogen by breaking down to glucose, but they don't actually use that glucose to form ATP.