Proline endopeptidase and exopeptidase activity in polymorphonuclear granulocytes.

Peptidases capable of releasing proline residues from polypeptides are present in the cytoplasmic fraction of rabbit polymorphonuclear granulocytes. This was shown with peptide substrates where proline is present either at the carboxy-terminal or within the polypeptide chain. Lysosomal and plasma membrane enzymes were inactive towards such polypeptides. The proline residue was hydrolyzed at either its amino end or its carboxy end. It is noteworthy that a Pro:Pro bond was cleaved both in the pentapeptide Thr-Lys-Pro-Arg and the dipeptide Pro:Pro.