Their functionality is exactly opposite. So this bifunctional enzyme can exist in two states. So State A or State B? In state A the phosphorptokinase to this structure is active while this one is inactive. And the reason it's active is because this serene residue found on this region here is not actually phosphorylated. Now, if protein kinase A takes an ATP and phosphorylates that serine residue on this domain, we create state B and in state B this becomes inactive while the other one becomes active.