Rat endothelin-converting enzyme-1 forms a dimer through Cys(412) with a similar catalytic mechanism and a distinct substrate binding mechanism compared with neutral endopeptidase-24.11

Endothelin-converting enzyme-1 (ECE-1) is involved in the conversion of big endothelins (big ETs) into endothelins (ETs) and shows sequence similarity with neutral endopeptidase-24.11 (NEP). Unlike NEP, ECE-1 exists as a disulphide-linked dimer. Here we reveal that Cys(412) is solely responsible for the dimerization of rat ECE-1. The C412S mutant enzyme, which existed as a monomer, showed no difference in glycosylation level, subcellular localization or clustering structure formation, but showed a higher K-m and lower k(cat) for big ET-1 compared with the wild-type enzyme. These results indicate that dimerization of ECE-1 is preferential for effective conversion of big ETs into ETs. In addition, complete loss of activity in the mutants E592Q, E651Q and H716Q confirmed that these residues are responsible for catalytic activity, zinc binding and stabilization of the intermediate during the transition state respectively. In contrast, the catalytic properties of mutant enzymes containing a substitution at Arg(129) or Glu(752) were not markedly different from those of the wild-type enzyme, suggesting that these residues play only a minor role, if any, in substrate binding, in contrast with their role in NEP.