A sensitive fluorimetric assay for serum angiotensin-converting enzyme

Am J Clin Pathol. 1976 Aug;66(2):416-24. doi: 10.1093/ajcp/66.2.416.


A simple, rapid, highly sensitive and reproducible assay for angiotensin-converting enzyme in untreated serum is described. It is based on the conversion of the substrate analog, hippuryl-L-histidyl-L-leucine (5 mM in 0.1 M K phosphate, pH 8.3-0.3 M NaCl) to hippurate and L-histidyl-L-leucine, which is quantified spectrofluorimetrically (lamdba excitation = 360 nm; lamdba fluorescence = 500 nm) by formation of a fluorescent adduct with ophthaldialdehyde. The chloride requirement and inhibition and activation patterns correspond to those for angiotensin-converting enzyme. The Km for hippuryl-L-histidyl-L-leucine was 1.33 mM. The mean value of serum angiotensin-converting enzyme for 58 normal human subjects (mean age, 32 years; range 19-57) was 32.2 +/- 1.30 (SE), with a standard deviation of 9.87 nmol/min/ml serum. The assay is useful for the diagnosis and possible management of sarcoidosis and may have other applications in the future.

MeSH terms

  • Humans
  • Kinetics
  • Peptidyl-Dipeptidase A / blood*
  • Peptidyl-Dipeptidase A / metabolism
  • Sarcoidosis / enzymology
  • Spectrometry, Fluorescence


  • Peptidyl-Dipeptidase A