Neutral proteinase inhibitors in PMN leukocytes. II. Isolation and characterization of a neutral proteinase inhibitor from porcine PMN leukocytes

An inhibitor of neutral proteinases was purified from porcine PMN leukocytes by gel filtration on Sephadex G-75 superfine and ion-exchange chromatography on Mono S. Thus an inhibitor preparation with a specific inhibitory activity against chymotrypsin of 10 IU/mg was obtained. In dodecyl sulfate gel electrophoresis a single protein band with an apparent molecular mass of 40 kDa was found under reducing conditions. Under non-reducing conditions the inhibitor forms higher molecular mass aggregates. On isoelectric focusing several protein bands with isoelectric points between pH 7.0 and 7.5 could be separated. The amino-acid composition of the inhibitory protein was determined. The inhibition mechanism was studied and association rate constants (kon) were measured and calculated for the reaction with chymotrypsin as well as leukocyte and pancreatic elastase. In Western blot analysis and in enzyme immunoassay studies crossreactivity between antibodies directed against porcine leukocyte neutral proteinase inhibitor and the corresponding inhibitor of bovine PMN leukocytes could be demonstrated.