Purification and characterization of endothelin-1 degradation activity from porcine kidney

In order to identify the membrane-bound peptidase that is responsible for the degradation of endothelin (ET), an endothelin-1 (ET-1) degradation enzyme was solubilized from membrane fractions of porcine kidney with 1% Triton X-100, and subsequently purified by column chromatographies, i.e., diethylamino-Sepharose ion exchange, gel permeation, Con A Sepharose and hydroxyapatite chromatography. On DEAE-Toyopearl ion exchange column chromatography, the ET degradation enzyme and aminopeptidase were separated, but ET degradation enkephalinase activities were not separable. In order to separate ET degradation enzyme and enkephalinase, the active fractions were loaded on each of the column chromatographies: sephacryl S-200, Con A Sepharose or hydroxyapatite. The ET degradation activities were co-migrated with enkephalinase activities on all of the three chromatographies. In addition, the ET degradation activities were inhibited by thiorphan, phosphoramidon and EDTA, which are known to inhibit enkephalinase. These results suggest that ET degradation activity in the membrane fractions of the kidney is related to enkephalinase and may be involved in the degradation of ET-1 in vivo.