Neutral proteases of human PMN leukocytes with kininogenase activity

A neutral protease with kininogenase activity was isolated from human polymorphonuclear (PMN) leukocytes by cation exchange chromatography and gel filtration. The protease appears heterogeneous by cation exchange chromatography, isoelectric focusing and cationic disc gel electrophoresis, but homogeneous by gel filtration, sucrose density gradient ultracentrifugation, SDS-disc gel electrophoresis and immunoelectrophoresis. By carrying out the electrophoresis of the protease in acrylamide gels of varying concentrations, it was shown that they represent charge isomers. The protease was stable at pH 4-10, but labile to heat, being almost completely inactivated when incubated for 30 min at 70 degrees C. It exhibited proteolytic activity between pH 5 and 9, being maximal at 7.5-8.5. The molecular weight of the PMN protease was estimated to be about 20,000 daltons by gel filtration in aqueous buffer and about 26,000-28,000 daltons by SDS-disc gel electrophoresis and gel filtration in Sepharose 6B in the presence of the dissociating agent guanidine HCl. Its sedimentation coefficient was about 2.7S. Corresponding to the charge heterogeneity, by isoelectric focusing, the kinin-generating and esterolytic activities of the PMN granule lysate focused between pH 6.0 and 11.5, whereas the isolated PMN protease focused between 10.0 and 11.8. With respect to kinin generation, caseinolysis, and alanine esterase activity, the protease was inhibited by DFP and certain chloromethyl ketone inhibitors, as well as the plasma protease inhibitory a1-antitrypsin, a2-macroglobulin and antithrombin III. Both bradykinin and a methionyl-lysyl-bradykinin-like peptide were generated from highly purified kininogens by a lysosomal lysate containing the PMN protease. However, this assay was done with a crude enzyme preparation which contains an aminopeptidase capable of converting lysyl-bradykinin or methionyl-lysyl-bradykinin to bradykinin. When injected intradermally, the protease induced hyperemia, hemorrhage, and moderate enhancement of vascular permeability, but the mixture of the protease and kininogen induced a marked enhancement of vascular permeability.