Cleavage of the Arg1-Pro2 bond of bradykinin by a human lung peptidase: isolation, characterization, and inhibition by several beta-lactam antibiotics.

An aminopeptidase P (EC 3.4.11.9) that cleaves the Arg1-Pro2 bond of bradykinin has been isolated for the first time from human lung and purified 473-fold. The enzyme also catalyzes the cleavage of arginine from des-[Arg9]-bradykinin and the hydrolysis of several X-proline dipeptides including L-arginyl-L-proline, L-leucyl-L-proline, and L-alanyl-L-proline. Purified enzyme was routinely assayed (after initial identification with des-[Arg9]-bradykinin) with L-leucyl-L-proline. The molecular weight, in nondenaturing buffers, is 188,000 +/- 8500 Da. The pH optimum was 8.0 with arginyl-proline, and was 6.8 with leucyl-proline. Chelating agents do not inactivate the enzyme, but rather only remove loosely bound cations that stimulate the enzyme. Manganese is the principal cation that stimulates the enzyme. The enzyme is inhibited by several beta-lactam antibiotics, cephalexin and oxacillin being the most effective of those tested. The antibiotic inhibition is time and temperature dependent, and it is not fully reversible by exhaustive dialysis of the antibiotic-treated enzyme.