Abstract
Dipeptidyl(amino)peptidase IV (DAP IV; EC 3.4.14.5) and post proline cleaving enzyme (PPCE; EC 3.4.21.26) can convert or degrade vasoactive peptides and have been identified in isolated vessels. The present study examined the cellular (endothelial/smooth muscle) localization of vascular DAP IV and PPCE. Membrane-bound DAP IV was higher on cultured hog aorta smooth muscle (11.7 +/- 1.7 nmol/min/mg) than on endothelium (1.5 +/- 0.3 nmol/min/mg). In contrast, comparable levels of cytosolic PPCE were found in endothelium and smooth muscle (1.5 +/- 0.3 and 1.8 +/- 0.3 nmol/min/mg, respectively). DAP IV was specifically inhibited by diprotin A (Ile-Pro-Ile) (IC50 = 6 microM) while PPCE was inhibited by TPCK. Neither enzyme was affected by o-phenanthroline or inhibitors of aminopeptidase M (amastatin, bestatin), neutral endopeptidases (phosphoramidon), carboxypeptidases N (MERGETPA) or ACE (captopril). DAP IV may play a role in the extracellular metabolism of peptides at or near endothelial and smooth muscle cell surface receptors. In contrast, the cytosolic localization of PPCE may limit its participation to intracellular peptide metabolism.
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