ACE-inhibitory activity assay: IC50

This protocol describes the procedure for the determination of the IC50 in inhibition on angiotensin-I converting enzyme (ACE) activity. ACE is also known as peptidyl dipeptidase A because it removes C-terminal dipeptides from a wide variety of peptide substrates. In the assay described here, the chosen substrate is the intramolecularly quenched fluorescent tripeptide o-aminobenzoylglycyl-p-nitrophenylalanylproline (Abz–Gly–Phe(NO2)–Pro). Hydrolysis of this substrate by the action of ACE generates the fluorescent product o-aminobenzoylglycine (Abz–Gly).