May protect procarboxypeptidase A against denaturation in the acidic environment of the ruminant duodenum. Monomer. The zymogen is secreted as a ternary complex composed of procarboxypeptidase A, chymotrypsinogen C and proproteinase E. Pancreas. Belongs to the peptidase S1 family. Defective elastase-like serine protease which does not seem to have protease activity.