And what happens is the sympathetic nervous system basically stimulates the adrenaline dula to release a hormone we call epinephrine. And as epinephrine travels through our cardiovascular system, it basically stimulates our cells to transform ATP molecules into another molecule known as cyclic adenosine monophosphate or simply camp. Now, what canp does is it's an allosteric regulator of protein kinase a and as we'll see in just a moment, it binds onto the inactive version of protein kinase A and it activates protein kinase A and protein kinase A. Once it's activated, it becomes responsible for activating many different types of enzymes via the process of phosphorylation. And it phosphorylates one of two types of residues either the serine residue or the Thurianine residue. Now, the question is on any given substrate enzyme molecule we have many different types of serene and three an amino acids.