And so what that means is it's ultimately the serine residue inside the active side. It's this residue here that acts as a nucleophile and will attack the carbon of the carbonyl that peptide bond nucleophilically. And we'll see exactly how that works out in just a moment. Now, the problem with Serene in this form shown here, is the side chain of Serene is in its alcohol form. And we know from organic chemistry that alcohols aren't very good nuclear files. So the problem here is this alcohol is not a strong nuclear file.