A SIMPLE ASSAY FOR THE MEASUREMENT OF CONVERSION OF BIG ENDOTHELIN-1 TO ENDOTHELIN-1 BY SMOOTH-MUSCLE

The conversion of exogenous big endothelin-l to endothelin-l by the smooth muscle of denuded porcine coronary arterial strips was measured by radioimmunoassay. Repeated incubations of a porcine coronary arterial strip with the same concentration of big endothelin-l yielded similar rates of conversion over a 4 h period. This property allowed the determination of a control rate of endothelin-l conversion by a coronary arterial strip followed by measurement of rates under various conditions. The assay described in this report can be used to investigate the biochemical properties and inhibitor profiles of the extracellular enzyme mediating the conversion of big endothelin-l to endothelin-l. The K-m and V-max of the enzyme were 34+/-2 mu M and 88+/-8 fmol/min, respectively. Cowas optimal at pH 7.0 and was inhibited by classic metalloprotease inhibitors.