Proline endopeptidase and exopeptidase activity in polymorphonuclear granulocytes

Area of Science:

• Biochemistry
• Cell Biology
• Enzymology

Background:

• Rabbit polymorphonuclear granulocytes are key immune cells involved in inflammatory responses.
• Understanding the enzymatic machinery within these cells is crucial for deciphering cellular processes.
• Proline residues play unique structural and functional roles in polypeptides.

Purpose of the Study:

• To investigate the presence and activity of peptidases releasing proline residues in rabbit granulocytes.
• To characterize the substrate specificity and cleavage sites of these proline-releasing enzymes.

Main Methods:

• Subcellular fractionation of rabbit polymorphonuclear granulocytes.
• Incubation of cytoplasmic fractions with synthetic peptide substrates containing proline.
• Analysis of peptide cleavage products to identify enzyme activity and specificity.

Main Results:

• Peptidases capable of releasing proline residues were identified in the cytoplasmic fraction.
• These enzymes demonstrated activity against substrates with carboxy-terminal or internal proline residues.
• Lysosomal and plasma membrane enzymes showed no activity against these proline-containing substrates.
• Proline hydrolysis occurred at both the amino and carboxy ends of the residue.
• Cleavage of a Pro:Pro bond was observed in both a pentapeptide and a dipeptide.

Conclusions:

• Rabbit granulocyte cytoplasm harbors specific peptidases for proline residue release.
• These enzymes exhibit broad substrate specificity, acting on internal and terminal proline.
• The identified peptidases are distinct from lysosomal and plasma membrane enzymes.
• The ability to cleave Pro:Pro bonds suggests a unique enzymatic capability within these cells.