And we also have thirianine proteases. So let's very quickly discuss these four of the five protease molecules. So let's begin with serine proteases. And by the way, the major difference between these different proteases is the presence of a specific type of residue inside the active side of that enzyme. So in the case of seren proteasis from the name you might guess that inside that active side it's a serene molecule, a serine amino acid that plays the nucleochilic role of nucleophilically attacking or breaking that peptide bond. And so it's the serine that ultimately catalyzes that reaction.