Evaluation of a kinetic assay for angiotensin converting enzyme

We have verified the analytical reliability of a Sigma reagent kit, which is a modified method of Holmquist et al. (1) for the determination of angiotensin-converting enzyme (ACE) on the Abbott ABA-100 analyzer. The reaction was linear up to 160 U/L. Correlation with a radiometric method (Ventrex Laboratories) was good except for a negative constant bias and loss of linearity with the radiometric method at high levels. The reconstituted reagent was determined by atomic absorption spectroscopy to contain 5.6 mumol/L of zinc. An increase in zinc content up to 45.6 mumol/L had little or no effect on enzyme activities of preparations from three mammalian species: rabbit, guinea pig and human. Neither was ACE activity inhibited by preincubating each of two serum pools with any of four corticosteroids for up to 8 d. Enzyme activity in samples remained stable at 5 degrees C for 8 d.