Properties of soluble and particulate angiotensin-converting enzymes of rabbit lung, induced macrophage and serum.

Rabbit serum, lung and corticosteroid-induced macrophage angiotensin-converting enzymes were compared with respect to migration on polyacrylamide-gel electrophoresis, sucrose gradient centrifugation and Km. Cellular particulate enzymes solubilized by nonidet P40 had approximately half the electrophoretic mobility of soluble enzymes and a similar Km (1.2 mM). Trypsin treatment of nonidet P40 solubilized particulate enzyme converted its electrophoretic mobility to that of soluble enzyme, and rendered it non-aggregating in sucrose gradients lacking detergent, similar to soluble enzyme. Approximate molecular weights by sucrose gradient centrifugation were similar for all enzymes (135,000-158,000). The data suggest that lung and macrophage enzymes are similar and that cellular particulate enzyme may be convertible to soluble enzyme.