Colorimetry of angiotensin-I converting enzyme activity in serum.
This simple, accurate, and reproducible colorimetric method for determining the activity of angiotensin-I converting enzyme is based upon colorimetry of the quinoneimine dye produced from the substrate p-hydroxyhippuryl-L-histidyl-L-leucine by action of this enzyme through the following series of reactions. The enzyme acts on the substrate to yield p-hydroxyhippuric acid and L-histidyl-L-leucine. The former is then hydrolyzed in the presence of hippuricase to produce p-hydroxybenzoic acid and glycine. Finally, oxidative coupling of p-hydroxybenzoic acid with 4-aminoantipyrine is catalyzed by peroxidase in the presence of hydrogen peroxide, producing a quinoneimine dye, the concentration of which is measured at its absorbance maximum at 505 nm to evaluate the activity of ACE. The Km value for the above-mentioned substrate is 0.32 mmol/L, the optimum pH is 8.3. Results by the present method and Cushman and Cheung's method (Biochem. Pharmacol. 20: 1637, 1971) correlate closely (r = 0.986). The within-run CV is 2.93%.
D003124:Colorimetry / Q000379:methods; D004492:Edetic Acid / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007703:Peptidyl-Dipeptidase A / Q000097:blood*; D014527:Uric Acid / Q000494:pharmacology
D014527:Uric Acid; D004492:Edetic Acid; D007703:Peptidyl-Dipeptidase A