Human lung post-proline endopeptidase: purification and action on vasoactive peptides

Area of Science:

• Biochemistry
• Enzymology

Background:

• Post-proline endopeptidase (PPE) is an enzyme implicated in peptide processing.
• Understanding PPE's substrate specificity and catalytic properties is crucial for its physiological relevance.

Purpose of the Study:

• To purify and characterize human lung post-proline endopeptidase (PPE).
• To investigate PPE's substrate specificity towards vasoactive peptides.
• To determine kinetic parameters and inhibition profiles of PPE.

Main Methods:

• Purification of PPE from human lung tissue.
• Enzyme activity assays using artificial substrates (e.g., Z-Gly-Pro-pNA).
• Determination of kinetic parameters (Km, Ki) and inhibition by various agents.

Main Results:

• PPE was purified with a specific activity 3,450 times higher than the starting material.
• The enzyme exhibited optimal activity at pH 7.4 and had a molecular mass of 77,000 Da.
• PPE demonstrated broad substrate specificity, cleaving vasoactive peptides including bradykinin, angiotensins I and II, substance P, and oxytocin.
• Inhibition studies revealed competitive inhibition by these peptides, with bradykinin showing the lowest Ki value.

Conclusions:

• Human lung PPE is a serine-dependent endopeptidase with significant activity against multiple vasoactive peptides.
• The enzyme's broad substrate specificity suggests a role in the regulation of peptide hormone and neurotransmitter levels.
• PPE's distinct inhibition profile from angiotensin-converting enzyme highlights its unique physiological function.