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Vascular, plasma membrane aminopeptidase M. Metabolism of vasoactive peptides
Abstract:
Aminopeptidase M (EC 3.4.11.2), an enzyme present on the cell surface of vascular endothelium and/or smooth muscle, rapidly hydrolyzes leucyl- and arginyl-2-naphthylamides and a number of vasoactive peptides at physiologic pH. Utilizing both thin-layer chromatography and high pressure liquid chromatography, it was found that vascular aminopeptidase M converted kallidin to bradykinin and inactivated des(Asp1)angiotensin I, angiotensin III, hepta(5-11)substance P and hexa(6-11)substance P. Aminopeptidase M did not, however, hydrolyze bradykinin, angiotensin I, angiotensin II, saralasin, vasopressin, oxytocin or any form of substance P containing a component of the Arg-Pro-Lys-Pro sequence. Both the naphthylamidase and peptidase activities were inhibited similarly by known amino-peptidase M inhibitors including o-phenanthroline, amastatin, bestatin and puromycin. However, inhibitors of angiotensin I converting enzyme (captopril), carboxypeptidase N (MERGETPA), neutral endopeptidase (phosphoramidon), post proline cleaving enzyme and dipeptidyl(amino)peptidase IV (diisopropylphosphofluoridate, DFP) were without effect. These results demonstrate that vascular, cell surface aminopeptidase M can selectively metabolize vasoactive peptides and may play a role in modulating their levels in the circulation and/or within the vessel wall.
Insights
Vascular aminopeptidase M metabolizes vasoactive peptides, converting kallidin to bradykinin and inactivating specific angiotensins and substance P fragments. This enzyme plays a role in regulating peptide levels within blood vessels.
Area of Science:
- Biochemistry
- Enzymology
- Vascular Biology
Background:
- Aminopeptidase M (APM) is a cell-surface enzyme found on vascular endothelium and smooth muscle.
- APM hydrolyzes various peptides at physiological pH, suggesting a role in vascular peptide metabolism.
Purpose of the Study:
- To investigate the specific vasoactive peptides metabolized by vascular aminopeptidase M.
- To determine the effect of APM on key peptides involved in blood pressure regulation.
- To differentiate APM activity from other peptidases using specific inhibitors.
Main Methods:
- Enzyme activity assays using leucyl- and arginyl-2-naphthylamides.
- High-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC) to identify peptide products.
- Testing the effects of known APM inhibitors and inhibitors of other peptidases.
Main Results:
- Vascular APM converted kallidin to bradykinin.
- APM inactivated des(Asp1)angiotensin I, angiotensin III, and specific substance P fragments.
- APM did not hydrolyze bradykinin, angiotensin I, angiotensin II, or substance P containing the Arg-Pro-Lys-Pro sequence.
- APM activity was inhibited by o-phenanthroline, amastatin, bestatin, and puromycin, but not by inhibitors of ACE, CPN, NEP, PPE, or DPP IV.
- Selective inhibition of APM confirmed its distinct peptidase activity.
Conclusions:
- Vascular aminopeptidase M selectively metabolizes specific vasoactive peptides.
- APM plays a significant role in modulating vasoactive peptide levels in the circulation and vessel wall.
- APM's distinct substrate specificity and inhibition profile differentiate it from other peptidases involved in peptide regulation.