Simplified Enzymatic Assay of Angiotensin-Converting Enzyme in Serum

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 estab-lished reaction catalyzed by y-glutamyltransferase (GGT; EC 2.3.2.2) to the ACE reaction, which releases glycyl-glycine 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 y-glutamyl group transferred from a donor substrate, L-’y-glutamyl-3-carboxy-4-ni-troanhlide.The reaction releases 3-carboxy-4-nitroaniline, which is monitoredspectrophotometncallyat 410 nm. The resulting rate of change inabsorbance islinearlyrelated tothe glycyl-glycineconcentrationand thereforetothe activityofACE. The linearangeof the method extend