Purification of a novel endothelin‐converting enzyme specific for big endothelin‐3

Abstract
Endothelin‐3 (ET‐3), a potent vasoactive peptide, is considered to be produced from big ET‐3 by endothelin‐converting enzyme (ECE) like the other members of the endothelin family (ET‐1 and ET‐2). We purified a novel ECE from bovine iris microsomes. The purified enzyme, a 140 kDa protein by SDS‐PAGE analysis, converted big ET‐3 to ET‐3 but not big ET‐1, with a K m value of 0.14 μM for big ET‐3. The conversion to ET‐3 was confirmed with sandwich EIA by monoclonal antibodies, the elution profile of HPLC, and intracellular calcium mobilization in CHO‐K1 cells expressing recombinant human ETB receptors. The conversion activity was inhibited by an inhibitor of neutral endopeptidase 24.11 (NEP) phosphoramidon. These results show that ECE‐3 purified from bovine iris is a novel metalloprotease totally different from ECE‐1 or ECE‐2, in that the enzyme is highly specific for big ET‐3.

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