Characterization of endothelin converting enzyme in rat lung

Area of Science:

• Biochemistry
• Enzymology
• Protease research

Background:

• Big endothelin (1-38) is a precursor peptide hormone.
• Endothelin (1-21) plays a crucial role in cardiovascular regulation.
• The specific enzymes responsible for big endothelin conversion in lung tissue are not fully characterized.

Purpose of the Study:

• To identify and characterize the enzyme responsible for converting human big endothelin (1-38) to endothelin (1-21) in rat lung plasma membranes.
• To determine the enzymatic properties, including optimal conditions and inhibitors.

Main Methods:

• Preparation of plasma membrane fraction from rat lung.
• Assay of enzyme activity using human big endothelin (1-38) as substrate.
• Enzyme inhibition studies with various protease inhibitors (Pepstatin-A, TLCK, Aprotinin, PMSF, E-64, Bestatin, Phosphoramidon, Thiorphan).
• Metal ion activation studies.

Main Results:

• An enzyme activity converting big endothelin (1-38) to endothelin (1-21) and a C-terminal fragment (CTF, 22-38) was identified in rat lung plasma membranes.
• The activity showed optimal function at pH 4.0.
• Pepstatin-A potently inhibited the enzyme (IC50 = 20 nM), while other tested inhibitors had no effect.
• Manganese (Mn+2), zinc (Zn+2), and calcium (Ca+2) ions activated the enzyme activity.

Conclusions:

• A Pepstatin-A inhibitable aspartic protease is likely involved in the conversion of big endothelin to endothelin in rat lung.
• Metal ion dependency suggests a metallo-aspartic protease may be responsible.
• This finding contributes to understanding endothelin processing pathways in the lung.