Metabolism of vasoactive peptides by vascular endothelium and smooth muscle aminopeptidase M.
The cellular localization of vascular plasma membrane aminopeptidase M (AmM; EC3.4.11.2) was examined in cultured porcine aorta endothelium and smooth muscle cells. AmM was 14-fold higher on smooth muscle (117 +/- 16 units/mg) than on endothelium (8.4 +/- 0.2). Proportional to its cellular distribution, AmM hydrolyzed the N-terminus of kallidin to produce bradykinin, and degraded des(Asp1)angiotensin I, angiotensin III, hepta(5-11)substance P and Met5-enkephalin. In contrast, bradykinin, angiotensin II and substance P were resistant to AmM-mediated hydrolysis. Peptide metabolism was optimal at pH 7.0 and was inhibited by o-phenanthroline, bestatin (Ki = 2.2 +/- 0.1 microM) and amastatin (Ki = 25 +/- 5 nM). Des(Asp1)angiotensin I and angiotensin III had the highest affinity (lowest Km) for AmM (Km = 2.2 +/- 0.5 and 2.0 +/- 0.4 microM respectively), followed by hepta(5-11)substance P (53.9 +/- 1.7 microM) and Met5-enkephalin (75.7 +/- 3.5 microM). In contrast, maximal velocities of hydrolysis were higher for Met5-enkephalin (313 +/- 2 nmol/min/mg) than for hepta(5-11)substance P (109 +/- 18 nmol/min/mg) or angiotensin III (26.5 +/- 1.0 nmol/min/mg). As expected for hydrolysis by a common enzyme, AmM-mediated enkephalin degradation was inhibited competitively by angiotensin III (Ki = 0.34 +/- 0.04 microM), hepta(5-11)substance P (43.7 +/- 6.3 microM) and kallidin (62 microM). These data suggest that vascular AmM may modulate vasoactive peptide levels in vivo, particularly within the microenvironment of endothelial and smooth muscle cell surface receptors.
Palmieri
F E
FE
Department of Pharmacology, New York Medical College, Valhalla 10595.
Bausback
H H
HH
Ward
P E
PE
D000626:Aminopeptidases / Q000032:analysis* / Q000037:antagonists & inhibitors; D000809:Angiotensins / Q000378:metabolism; D000818:Animals; D018826:CD13 Antigens; D002855:Chromatography, Thin Layer; D004730:Endothelium, Vascular / Q000201:enzymology*; D004743:Enkephalin, Leucine / Q000378:metabolism; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000201:enzymology*; D010455:Peptides / Q000378:metabolism*; D013373:Substance P / Q000378:metabolism; D013552:Swine
D000809:Angiotensins; D010455:Peptides; D013373:Substance P; D004743:Enkephalin, Leucine; D000626:Aminopeptidases; D018826:CD13 Antigens