The severed activation segment of porcine pancreatic procarboxypeptidase a is a powerful inhibitor of the active enzyme Isolation and characterisation of the activation peptide

The activation peptide of the monomeric procarboxypeptidase A from porcine pancreas was isolated by means of controlled trypsin digestion of the proenzyme followed by ion-exchange chromatography under dissociating conditions (7 M urea). The molecular weight of the isolated peptide was estimated to be around 11500-12000 (corresponding to approx. 100-103 residues) as judged by SDS electrophoresis and amino acid analysis, a figure that agrees with the difference between the corresponding values for procarboxypeptidase A and carboxypeptidase A (peptidyl-l-amino-acid hydrolase, EC 3.4.17.1). The activation peptide has a high content of hydrophobic and acidic amino acids, and lacks cysteine. A remarkable feature is the strong competitive inhibitory action of the peptide on both porcine and bovine pancreatic carboxypeptidase A activity, with a Ki in the nanomolar range, and its null ability to inhibit porcine pancreatic carboxypeptidase B (EC 3.4.17.2). The above properties, and the fact that the peptide has the same N-terminal residue (lysine) as the parent procaboxypeptidase A, suggest that the isolated peptide contains most (if not all) of the activation segment of the proenzyme. © 1982.