So as we mentioned previously, under stressful situations the Adrian medulla is stimulated and it releases the epinephrine hormone. And the epinephrine hormone basically stimulates the production of cyclic adenosine monophosphate camp. And it's the Tamp that is the allosteric regulator of PKA. The question is how exactly does it regulate the activity and how does it activate this enzyme? So what happens is, if we examine a single one of these regulatory chains each regulatory chain contains one, two allosteric sites. So we have one, two, and two here.