EVIDENCE THAT ENZYMATIC CONVERSION OF N-[1(R,S)-CARBOXY-3-PHENYLPROPYL]-ALA-ALA-PHE-P-AMINOBENZOATE, A SPECIFIC INHIBITOR OF ENDOPEPTIDASE 24.15, TO N-[1(R,S)-CARBOXY-3-PHENYLPROPYL]-ALA-ALA IS NECESSARY FOR INHIBITION OF ANGIOTENSIN-CONVERTING ENZYME

N-[ 1 (R,S)-Carboxy-3-phenylpropyl]-Ala-Ala-Phe-p-aminobenzoate (cFP-AAF-pAB) is a potent, substrate-related, specific inhibitor of endopeptidase 24.15, an enzyme involved in the metabolism of bioactive peptides including bradykinin, neurotensin, and proenkephalin, and prodynorphin-derived enkephalin precursors. The observation that this inhibitor causes a pronounced decrease in blood pressure after intravenous infusion into normotensive rats posed the question of the mechanism of this hypotensive response. It was suggested previously that cFP-AAF-pAB is an inhibitor of angiotensin converting enzyme (ACE) and that this function can account for the hypotensive response to the inhibitor. We present here evidence that cFP-AAF-pAB has no intrinsic ACE-inhibitory activity. The previously observed inhibition is shown to be dependent on cleavage of the Ala-Phe bond in the inhibitor by endopeptidase 24.11 (enkephalinase, EC 3.4.24.11), a contaminant of some ACE preparations.