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? So I've listed six different categories, six different types of enzymes. So category one and two we're going to focus on in much more detail in the next several lectures. And three to six, we're going to focus briefly only in this lecture.