Inhibitor potencies and substrate preference for endothelin-converting enzyme-1 are dramatically affected by pH

Area of Science:

• Biochemistry
• Enzymology
• Pharmacology

Background:

• Endothelin-converting enzyme-1 (ECE-1) is a metalloprotease involved in the processing of various peptide hormones.
• Phosphoramidon, a known ECE-1 inhibitor, exhibits significant pH-dependent inhibition.
• The pH optimum for ECE-1 activity is generally considered to be neutral, unlike the acidic optimum for ECE-2.

Purpose of the Study:

• To investigate if the pH-dependent inhibition of ECE-1 is a general phenomenon.
• To determine the effect of pH on the activity and substrate preference of ECE-1.
• To explore the implications of pH-dependent substrate preference for ECE-1 specificity in vivo.

Main Methods:

• Tested two structurally distinct ECE-1 inhibitors, PD 069185 and CGS 31447, across a range of pH values.
• Assessed ECE-1 inhibition by measuring enzyme activity at different pH conditions.
• Analyzed the pH optima for ECE-1 hydrolysis of different substrates, including big ET-1, bradykinin, and substance P.

Main Results:

• The potencies of both PD 069185 and CGS 31447 as ECE-1 inhibitors were found to be highly pH-dependent.
• ECE-1 demonstrated a substrate-dependent pH optimum for activity.
• While ECE-1 showed a neutral pH optimum with big ET-1, it exhibited acidic pH optima (5.6-5.8) when hydrolyzing bradykinin and substance P.

Conclusions:

• The pH-dependence of ECE-1 inhibition extends to structurally diverse inhibitors.
• ECE-1's substrate preference is significantly influenced by pH, challenging the notion of a single neutral pH optimum.
• This pH-mediated substrate selectivity may represent a mechanism for regulating ECE-1 specificity in biological systems.