Enzyme Assay: Human aminopeptidase P2 (APP2) enzyme activity was determined using the internally quenched fluorescent substrate: H-Lys(2-aminobenzoyl)-Pro-Pro-p-nitroanilide (Bachem, Torrance, Calif.) at 1 μM (=Km) for inhibitor studies and 5 μM for enzyme purification assays. The assay buffer was 0.1 M HEPES, pH 7.4, and the assay temperature was 30° C. Cleavage of the substrate by the enzyme produces an increase in fluorescence due to the release of H-Lys(2-aminobenzoyl). Enzyme rates were determined in an F. fluorescence plate reader (Molecular Devices, Sunnyvale, Calif.) using an excitation wavelength of 320 nm and an emission wavelength of 405 nm.
Enzyme Assay: Human recombinant angiotensin-converting enzyme (hrACE) was obtained from R&D Systems (Minneapolis, Minn.). Its enzyme activity was determined using the internally quenched fluorescent substrate ES005: (7-methoxycoumarin-4-yl)acetyl-Arg-Pro-Pro-Gly-Phe-Ser-Ala-Phe-(2,4-dinitrophenyl)-Lys (R&D Systems, Minneapolis, Minn.). The assay buffer was 0.1 M HEPES, pH 7.4, and the temperature was 30° C. The substrate concentration was below Km (≦40 μM). Enzyme rates were determined in an Fmax fluorescence plate reader (Molecular Devices, Sunnyvale, Calif.) using an excitation wavelength of 320 nm and an emission wavelength of 405 nm.