Hydrolysis of bradykinin by angiotensin-converting enzyme.

Two dipeptides, phenylalanylarginine (Phe-Arg) and serylproline (Ser-Pro), are released sequentially from bradykinin by angiotensin-converting enzyme purified from hog lungs; chloride increases the rate of release of both dipeptides. Using an automated ninhydrin-reagent method, we studied the kinetics of bradykinin hydrolysis. The reaction proceeded in the absence of chloride; however, the addition of chloride increased the rate of hydrolysis by decreasing Km and increasing Vm . The Km values for bradykinin were 3.9 x 10~M in the absence of chloride and 0.85 x 10~M in the presence of 0.01M NaCl (optimal concentration). Both of these Km values were well below the value of 30 x 10" M determined for angiotensin I at its optimal chloride concentration of 0.1M. Hydrolysis of bradykinin had a pH optimum of 7 and was inhibited by low concentrations (10~M) of ethylenediaminetetraacetic acid or the nonapeptide pyroglutamyl (Pyr)-Trp-ProArg-Pro-Gln-Ile-Pro-Pro. It is concluded that one enzyme, acting as a dipeptidyl carboxypeptidase, catalyzes both the conversion of angiotensin I to angiotensin II and the hydrolysis of bradykinin.