Urea-gradient gel electrophoresis studies on the association of procarboxypeptidases A and B, proproteinase E, and their tryptic activation products.

Monomeric procarboxypeptidase A (PCPA) and isolated proproteinase E (PPE), both from pig pancreas, were shown by means of electrophoresis on transverse urea gradients (0-9 M) to form a very stable complex, identical to their natural binary complex. Although the complex is maintained by the interaction of both active regions, the activation segment of PCPA participates directly in the binding. Procarboxypeptidase B (PCPB) also associates with PPE, but in this case the complex shows low stability. In contrast with carboxypeptidases A that strongly bind to their corresponding severed activation segments, no interaction was observed between carboxypeptidase B and its severed activation segment. The above results give some insight into several characteristics of the structure and activation properties of pancreatic PCPA and PCPB.