title: Angiotensin metabolism by cerebral microvascular aminopeptidase A.
abstract: Porcine cerebral microvessels were isolated by differential sieving and centrifugation and were characterized by microscopic examination and marker enzyme enrichment (gamma-glutamyltransferase; EC 2.3.2.2). Purified microvessels contained a membrane-bound enzyme immunologically indistinguishable from renal aminopeptidase A (AmA; EC 3.4.11.7). AmA hydrolyzed both alpha-glutamyl- and alpha-aspartyl-2-naphthylamide, and hydrolysis was competitively inhibited by angiotensin II. Micro-vessel AmA hydrolyzed the N-terminal Asp1-Arg2 bond of both angiotensin I and angiotensin II, whereas the angiotensin II antagonist saralasin [(Sar1, Ala8)angiotensin II] was resistant to N-terminal hydrolysis. Angiotensin metabolism was optimal at pH 8.5 and was inhibited by EDTA, o-phenanthroline and amastatin. Conversely, inhibitors of neutral endopeptidase (phosphoramidon), post-proline cleaving enzyme (Z-Pro-Prolinal), carboxypeptidase N [D-L-mercaptomethyl-3-guanidinoethylthiopropanoic acid (MERGETPA)] and angiotensin I converting enzyme (captopril) had no effect. The Km values of angiotensin I, angiotensin II and (Asn1, Val5)angiotensin II for microvessel AmA were 40.1 +/- 8.2, 35.3 +/- 4.3 and 156 +/- 22 microM respectively. Cerebral microvascular aminopeptidase A may play a role in vivo in modulating angiotensin-mediated local cerebral blood flow, and in preventing circulating angiotensins from crossing the blood-brain barrier.
mesh_terms: D000626:Aminopeptidases / Q000378:metabolism*; D000803:Angiotensin I / Q000378:metabolism*; D000804:Angiotensin II / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000201:enzymology*; D002560:Cerebrovascular Circulation; D043384:Glutamyl Aminopeptidase; D007700:Kinetics; D008833:Microcirculation / Q000201:enzymology; D013379:Substrate Specificity; D013552:Swine; D005723:gamma-Glutamyltransferase / Q000378:metabolism
chemical_list: D000804:Angiotensin II; D000803:Angiotensin I; D005723:gamma-Glutamyltransferase; D000626:Aminopeptidases; D043384:Glutamyl Aminopeptidase