Endothelin-converting enzyme: the binding of metal ions.

The metal ion of endothelin-converting enzyme (ECE) was investigated by inhibiting the enzyme with ethylenediaminetetraacetic acid (EDTA) and restoring activity by adding divalent metal salts in quantities less than the concentration of EDTA. Under these conditions, only metal ions that bind to ECE with high affinity can affect the enzyme. The ferrous enzyme had an activity of 76% relative to the native enzyme, the manganous enzyme 76%, the nickelous enzyme 77%, the cupric enzyme 17%, the zinc enzyme 98% and the cobaltous enzyme 122%. Of these first transition series elements only zinc can be the metal of the native enzyme. The zinc enzyme has the same Km and turnover number as the native enzyme.