Human endothelin converting enzyme isolated from blood or placenta by hydrated density

Human endothelin converting enzyme (ECE) has been isolated from blood or placenta by a series of centrifugation steps at different densities. A first ECE-I is isolated by a low speed centrifugation to produce enzyme with a hydrated density of about 0.94 g/ml. A second high speed centrifugation produces an ECE-II with a hydrated density between about 0.94 to about 1.006 g/ml. After adjusting the density of the solution, a high speed centrifugation isolates an ECE-III with a hydrated density between about 1.006 to about 1.063. A final adjustment to the density of the solution and high speed centrifugation obtains an ECE-IV with a hydrated density of between about 1.063 to about 1.210 g/ml.