A sensitive fluorimetric assay for serum angiotensin-converting enzyme.

Area of Science:

• Biochemistry
• Enzyme Assays
• Clinical Diagnostics

Background:

• Angiotensin-converting enzyme (ACE) plays a crucial role in the renin-angiotensin system.
• Accurate measurement of ACE activity in serum is important for diagnosing and managing certain diseases.

Purpose of the Study:

• To develop and validate a simple, rapid, sensitive, and reproducible assay for quantifying angiotensin-converting enzyme (ACE) activity in untreated human serum.

Main Methods:

• The assay utilizes the substrate hippuryl-L-histidyl-L-leucine, measuring the product hippurate spectrofluorimetrically after reaction with ophthaldialdehyde.
• Optimized conditions include 5 mM substrate in 0.1 M potassium phosphate buffer (pH 8.3) with 0.3 M NaCl.
• Enzyme kinetics were determined, with a Km of 1.33 mM for the substrate.

Main Results:

• The assay demonstrated chloride dependence and characteristic inhibition/activation patterns consistent with ACE.
• The mean serum ACE level in 58 healthy individuals (age range 19-57) was determined to be 32.2 ± 1.30 nmol/min/ml serum (SD = 9.87).

Conclusions:

• The developed assay provides a reliable method for measuring serum ACE activity.
• This assay is valuable for the diagnosis and management of sarcoidosis and may find broader clinical applications.