title: Enzymes in placental microvilli: angiotensin I converting enzyme, angiotensinase A, carboxypeptidase, and neutral endopeptidase ("enkephalinase").
abstract: Microvilli from human placental syncytiotrophoblast are rich in angiotensin I converting enzyme (ACE), aminopeptidase A, a carboxypeptidase N-like enzyme, and a neutral endopeptidase (NEP). The specific activities of these enzymes were enhanced in microvillus-enriched fractions obtained by differential centrifugation: Purified microvilli were isolated in a discontinuous sucrose gradient. The placental microvilli hydrolyzed angiotensin II, vasopressin and oxytocin as shown by high pressure liquid chromatography. The inhibitors, bestatin, phosphoramidon, and o-phenanthroline, established the specificity of the enzymes. Aminopeptidase A (angiotensinase A) cleaved angiotensin II to angiotensin III and Asp1. NEP from placenta and from human kidney hydrolyzed oxytocin at the Pro7-Leu8 bond to yield oxytocin 1-7 and leucyl-glycine amide, but did not hydrolyze vasopressin. Vasopressin was cleaved by aminopeptidases in the placental membranes. On electroblotting placental NEP appeared as a double band with a molecular weight slightly higher than the 90,000 of the purified kidney enzyme. Neuraminidase treatment reduced the molecular weight of the placental enzyme to approximately 90,000, indicating that it contains a large amount of sialic acid. The microvilli of human placenta are thus rich in enzymes that may regulate passage of peptides at the maternal-fetal interface.
mesh_terms: D000626:Aminopeptidases / Q000302:isolation & purification* / Q000378:metabolism; D002268:Carboxypeptidases / Q000302:isolation & purification* / Q000378:metabolism; D002458:Cell Fractionation; D010450:Endopeptidases / Q000302:isolation & purification* / Q000378:metabolism; D005260:Female; D043384:Glutamyl Aminopeptidase; D006801:Humans; D007700:Kinetics; D008871:Microvilli / Q000201:enzymology*; D015260:Neprilysin; D007703:Peptidyl-Dipeptidase A / Q000302:isolation & purification* / Q000378:metabolism; D010920:Placenta / Q000201:enzymology*; D011247:Pregnancy
chemical_list: D002268:Carboxypeptidases; D010450:Endopeptidases; D000626:Aminopeptidases; D043384:Glutamyl Aminopeptidase; D007703:Peptidyl-Dipeptidase A; D015260:Neprilysin