On the other hand, unlike phosphorylation, proteolytic activation does not require ATP. And what that means those enzymes and proteins which are found outside our cells in the extracellular environment can readily undergo the process of proteolytic activation. Now unlike allosteric regulation and covalent modifications such as phosphorylation, which can take place many times on any given enzyme, when a zymogen undergoes proteolytic activation it will only undergo this process once in the lifetime of that enzyme. So once again, proteolytic activation does not require ATP, adenosine, triphosphate and so it can readily take place outside the cells. In addition, enzymatic proteolysis only occurs once in the lifetime of that enzyme. Now the next question I want to explore is what are some examples of enzymes, biological proteins found inside our body that utilize the process of proteolytic activation?