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Clinical Chemistry 39: 400-404, 1993;
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Clinical Chemistry, Vol 39, 400-404, Copyright © 1993 by American Association for Clinical Chemistry

Simplified enzymatic assay of angiotensin-converting enzyme in serum

JL Groff, JB Harp and M DiGirolamo
Department of Medical Technology, Georgia State University, Atlanta 30303.

We report a simple, enzymatic method for determining angiotensin- converting enzyme (ACE; EC 3.4.15.1) in serum. The proposed method features coupling an established reaction catalyzed by gamma- glutamyltransferase (GGT; EC 2.3.2.2) to the ACE reaction, which releases glycylglycine from the artificial substrate hippuryl-glycyl- glycine. The glycyl-glycine released by the ACE reaction becomes rate- limiting in the GGT reaction, in which it participates as a receptor substrate for a gamma-glutamyl group transferred from a donor substrate, L-gamma-glutamyl-3-carboxy-4-nitroanilide. The reaction releases 3-carboxy-4-nitroaniline, which is monitored spectrophotometrically at 410 nm. The resulting rate of change in absorbance is linearly related to the glycyl-glycine concentration and therefore to the activity of ACE. The linear range of the method extends from ACE values < 50 to at least 1300 U/L of serum. Good precision is indicated by a low CV for replicate analyses (3.6% and 4.6% for within-run and day-to-day assays, respectively, for normal ACE activity, and 3.1% within-run for high ACE activity). Results also correlate well with those of an established colorimetric method (r = 0.978). The major advantages of the method are its procedural simplicity, limited cost, use of readily available reagents, applicability to isoenzyme studies, and adaptability to automation.




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Copyright © 1993 by the American Association for Clinical Chemistry.