Figure 24.6 Phosphorylase regulation. Both phosphorylase b and phosphorylase a exist in equilibrium between an active R state and a less active T state. phosphorylase b is usually inactive because the equilibrium favors the T state. phosphorylase a is usually active because the equilibrium favors the R state. In the T state, the active site is partly blocked by a regulatory structure. The active site is unobstructed in the R state. regulatory structures are shown in blue and green.