The activation peptide of pancreatic procarboxypeptidase A is the keystone of the bovine procarboxypeptidase A-S6 ternary complex.

In some ruminant species, pancreatic procarboxypeptidase A is the central element of a ternary complex involving two other components, a C-type chymotrypsinogen and an inactive protease E. Although the complex is devoted to protein digestion, the fate of this system upon activation of its constituent subunits has, as yet, not been clearly established. In this paper, the activation peptide of procarboxypeptidase A is shown to play a key role in the association of the three subunits and a model is proposed for the in vivo function of the complex.