Abstract
The development and validation of two different assays for serum angiotensin-converting enzyme are reported. The first step in both analytical systems is based on enzymatic cleavage of the synthetic substrate, hippuryl—histidyl—leucine, under conditions advocated by Cushman and Cheung. The hippuric acid released is then assayed either by colorimetry following an azlactone condensation reaction with an aromatic aldehyde, or by reversed-phase ion-pair high-performance liquid chromatography (HPLC). Both procedures reveal good linearity in the range 0–80 nmol/ml per min, with an inter-assay coefficient of variation of 6·2% for the colorimetric assay and 4·5% for the HPLC-assisted assay. Recovery values measured for the colorimetric method ranged from 97% to 102% and for the HPLC-assisted method from 98% to 101%. The colorimetric method is suitable for performance in small hospital laboratories since it can be carried out with simple analytical instrumentation. It is obvious nevertheless, that the HPLC-assisted assay reveals better validation criteria. The method is also simple and rapid and it has successfully been used in our laboratory for the last two years.