The Reactive Site of the Basic Trypsin Inhibitor of Pancreas

Abstract

Abstract The basic trypsin inhibitor of bovine pancreas (Kunitz and Northrop inhibitor) has five amino groups, provided by a single NH2-terminal arginyl residue and 4 lysyl residues. When the free inhibitor is allowed to react with N-carboxy-dl-alanine anhydride all five amino groups are blocked. In contrast, when the reaction is performed with the trypsin-bound inhibitor, lysine 15 is unmodified and therefore is shielded by trypsin in the complex. It may be concluded that this lysyl residue is involved in the interaction between inhibitor and trypsin.