KRISHNAMURTI DEMORAISCARVALHO*, CARINEJOUDIOU, HAMADIBOUSSETTA, ANNE-MARIELESENEY, AND PAULCOHEN

Anendopeptidase wasisolated fromXenopus laevis skinsecretions. Thisenzyme, whichhasanapparent molecular massof100kDa,performs aselective cleavage atthe Xaa-Phe, Xaa-Leu, orXaa-Ile bond(Xaa=Ser, Phe, Tyr, His, orGly)ofanumberofpeptide hormones, including atrial natriuretic factor, substance P,angiotensin H,bradykinin, somatostatin, neuromedins BandC,andlitorin. Thepeptidase exhibited optimal activity atpH7.5andaKminthemicromolar range. Nocleavage wasproduced invasopressin, ocytocin, minigastrin I,and(Leu5Jenkephalin, whichinclude intheir sequence anXaa-Phe, Xaa-Leu, orXaa-Ile motif. Theen- dopeptidase activity wasinhibited bydivalent cation chelators andbyphosphoramidon only athigh concentrations (ICss = 50 jAM), whereas itwas insensitive toclassical inhibitors of chymotrypsin, angiotensin convertase, andserine andcysteine peptidases, aswell ascarboxypeptidases. Itishypothesized that this enzyme, which isdistinct fromneutral endopeptidase (EC 3.4.24.11), constitutes theprototype ofafamily ofrelated metalloendopeptidases thatinactivate peptide substrates by cleavage attheXaa-Phe, Xaa-Leu, orXaa-fle bond. Arather limited number ofpeptidases seemtobeinvolved in thepostsecretory inactivation ofpeptide hormone messen- gers. Theimportance ofthese proteolytic mechanisms in regulating hormonal action canbedemonstrated bythefact thattheir effects canbeprolonged invivoorinvitro by selective inhibitors ofthese enzymes. This hasbeenshownin thecaseoftheenkephalin-degrading