And out of these three amino acids, it's the serine that acts as the nucleophilic agent. Now, what about the other categories of proteases? So remember, we not only have seren proteases, but we also have cysteine proteases aspertal proteases metalloprotiases. And we have other examples of proteases that we're not going to focus on in this lecture. So the question is, what exactly is the mechanism of these other proteases? And how does the mechanism differ or how does it compare to the mechanism inside seren proteases?