Endothelin-converting enzyme activity in human serum lipoprotein fraction

Area of Science:

• Biochemistry
• Cardiovascular Research
• Enzymology

Background:

• Endothelin-1 (ET-1) is a potent vasoconstrictor.
• The conversion of big ET-1 to active ET-1 is a critical regulatory step.
• Endothelin-1 (ET-1)-converting enzyme (ECE) activity in serum is not fully understood.

Purpose of the Study:

• To investigate the presence and characteristics of ECE activity in human serum lipoproteins.
• To determine the contribution of lipoproteins to overall serum ECE activity.
• To elucidate the properties and potential inhibitors of lipoprotein-associated ECE.

Main Methods:

• Enzyme immunoassay for sensitive detection of ECE activity.
• Reverse-phase high-performance liquid chromatography (RP-HPLC) for enzyme characterization.
• Assay of synthetic human big ET-1 cleavage by serum lipoprotein fractions.

Main Results:

• Serum lipoprotein fractions exhibited approximately 14-fold higher ECE activity compared to whole serum.
• Lipoprotein-associated ECE activity was optimal at pH 7.0.
• The enzyme activity was inhibited by metalloproteinase and chymotrypsin-like inhibitors, but not by cysteine or aspartic proteinase inhibitors.

Conclusions:

• Human serum lipoproteins possess significant ECE activity, crucial for big ET-1 conversion.
• Lipoprotein-associated ECE activity suggests a role in regulating ET-1 levels in circulation.
• The enzyme's properties indicate it is a metalloproteinase with chymotrypsin-like characteristics.