A Scheme for Determining the Correct Activityof the KineticAngiotensin- Converting Enzyme

The absorbance difference measured when angiotensin-convertingenzyme (EC 3.4.15.1) hydrolyzes the substrate N-[3-(2-furyl)acryloyl]-L-phenylalanylglycylglycine is the basis for measuring its activity. We show this difference to be instrument dependent, and describe a method for deriving it that is applicable to manual or automated procedures. Addftlonal Keyphrases: enzymeactivity. analytical error Kinetic spectrophotometry of angiotensin-converting en-zyme (ACE; EC 3.4.15.1), ’ first proposed by Holmquist et al. (1) and later used for determining ACE activity in human serum (2), appears simple and suitable for the clinical laboratory. Recently, this method has been adapted for the Multistat ifi centrifugal analyzer (3) and the Olli C Com-pact Clinical Analyzer (4). The method involves hydrolysis of the substrate, N-[3-(2