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. So let's suppose we have a sequence of 200 amino acids and let's say 20 of them are actually serene or three Anion amino acids. The question is how does protein kinase A actually know which Serine or three an amino acid to actually bind to? What determines the specificity of that protein kinase A?