In building the glycogen molecule it helps control the rate of glycogen synthesis. So this enzyme, glycogen synthase, actually exists in two different forms. We have glycogen synthase A and glycogen synthase B. Now the only difference between these two enzymes is the fact that glycogen synthase B is simply the phosphorylated version of glycogen synthase A. Now glycogen synthase A always exists in the fully active form. Now glycogen synthase B is predominantly in the inactive form but under certain molecules.