A covalent serine protease inhibitor—Na-p-Tosyl-Lysyl Chloromethylketone (TCK) is a modified lysine residue tosylated at the N-terminus and chloromethylated C-terminus, one molecule of which capable forming two bonds with both Ser His catalytic residues, was co-crystallized oligopeptidase B (OpB) from Serratia proteomaculans (PSPmod). The kinetics study, preceded crystallization, shows that sto...