At the end of any enzyme, catalyzed react. Remember, enzymes are never changed or depleted at the end of the reaction. They always have to be regenerated. And that's why this bond is only a temporary covalent bond. Now, we said earlier that Chimetrypin is an example of a Serene protease. And what that means is inside the active side of that Chimetrypsin, it's the serine molecule, the serine amino acid, that plays the role of the powerful nuclear fide that catalyzes the cleavage of that peptide bond.