Conformations of chymotrypsinogen and chymotrypsin. The electrostatic interaction between the α-amino group of isoleucine 16 and the carboxylate of aspartate 194, essential for the structure of active chymotrypsin, is possible only only after cleavage of the peptide bond between isoleucine and arginine in chymotrypsinogen.
[Information from Gregory A. Petsko and Dagmar Ringe, Protein Structure and Function (Sinauer, 2003), p. 3- 3-