Fluorometric assay for angiotensin converting enzyme in human serum by centrifugal analysis.

Due to its action on angiotensin I and bradykinin, angiotensin converting enzyme (ACE, dipeptidyl carboxypeptidase, EC 3.4.15.1) plays a crucial role in blood pressure regulation [l]. Attention was focused on this enzyme when Lieberman observed elevated serum ACE levels in active sarcoidosis [2]. Because ACE is a sensitive index both in assessing the clinical status of this disease and in monitoring corticosteroid therapy [3-S], it has become an indispensable parameter in the difficult diagnosis of sarcoidosis [2]. Here we describe a one-step fluorometric assay for ACE, based on ACE-catalysed hydrolysis of the intramolecularly quenched fluorogenic substrate o-aminobenzoylglycyl-p-nitro-L-phenylalanyl+proline (Abz-Gly-Phe(NO*)-Pro) [6], which involves only one stable reagent. Due to the minimal amount of reagent required (100 pl), its high precision, and its simplicity, this assay is readily applicable to automated analysis by means of a fluorescence centrifugal analyser.