LIVER BRADYKININ-INACTIVATING-ENDOPEPTIDASE IS SIMILAR TO THE METALLOENDOPEPTIDASE (EC-3.4.24.15)

The bradykinin-inactivating-endopeptidase (BIE) removal from rat liver , by perfusing the organ with 0.05% Triton X-100, achieved its maximum at 10 min of perfusion and falls to 50% of the maximum in 30 min, a p attern similar to AST removal. Using an internally quenched fluorescen t BK analogue (Abz-RPPGFSPFRQ-EDDnp) we further characterized this enz yme: it is activated by low concentrations of 2-mercaptoethanol, inhib ited by p-hydroxymercuribenzoate, o-phenanthroline and EDTA, and is re sistant to enalapril, E-64 and PMSF. These results suggest that BIE is a metalloendopeptidase containing a thiol group important for its act ivity. BIE also hydrolyses the peptides Abz-GGFLRRVQ-EDDnp, Abz-GPQGLA GQ-EDDnp, Abz-FRSVQ-EDDnp, and Abz-ARVRRANSFLQ-EDDnp. All these proper ties are very similar to those described or assayed by us for EC 3.4.2 4.15, isolated initially from rat testes and then from several organs of different animals. Both BIE and EC 3.4.24.15: hydrolyze the (FS6)-S -5 bond of the BK fluorescent substrate; are efficiently inhibited by Orlowski specific inhibitor (CFP-AAF-pAB, K-i 4.4 x 10(-7) M and 1.25 x 10(-7) M, respectively); have the same electrophoretic mobility in S DS-PAGE (M(r) 78 000); and are both recognized by three polyclonal ant ibodies raised against rat testes EC 3.4.24.15. In conclusion, BIE app ears to be EC 3.3.24.15.