Differential inhibition of wild-type endothelin-converting enzyme-1 and its mutants

The purpose of this study was to determine the effect of mutation of rat endothelin-converting enzyme-1 (ECE-1) on the potencies of various inhibitors. The two amino acids mutated were Cys(412), which was shown to link the two monomeric enzymes to form a dimer, and Glu(752), postulated to be involved in substrate and inhibitor binding. No significant effects were noted when Glu(752) was replaced by an acidic (E752D) or uncharged (E752Q) residue. Replacing Glu(752) by a basic residue (E752R) slightly weakened the potencies of the inhibitors. In contrast, a significant decrease in the potencies was observed with the monomeric enzyme C412S. Phosphoramidon inhibited the wild-type ECE-1 with an IC50 of 1.5 microM, but it was about sixfold weaker for the C412S mutant. CGS 31447, an aminophosphonic acid, inhibited the wild-type and C412S enzymes with IC50 values of 5.8 and 76 nM, respectively. A similar degree of change in the potencies was also seen with CGS 25015, a thiol-containing compound, which inhibited the respective enzymes with IC50 values of 17 and 190 microM. These results suggest that the charge in Glu(752) may not be important for inhibitor binding and that the dimeric ECE-1 is more susceptible to inhibition than the monomeric enzyme.