Generation of a subunit III-like protein by autolysis of human and porcine proproteinase e in a binary complex with procarboxypeptidase A

Tryptic treatment of human and porcine proproteinase E, procarboxypeptidase A binary complexes gave rise to active proteinase E after removal of an 11-residue N-terminal activation peptide. By contrast, upon treatment of either complex with active proteinase E, not only was the activation peptide released but also the hydrophobic dipeptide Val12-Val13 of the corresponding enzyme. No serine protease activity on specific synthetic peptide substrates could be detected. The structural homology of inactive proteinase E with subunit III of ruminant procarboxypeptidase A was strengthened by the existence of a functional homology since truncated proteinase E still possessed a weakly functional active site. Thus, subunit III-like proteins are generated by proteinase E-catalyzed limited proteolysis of proproteinase E.