Chymotrypsin-like Neutral Protease from Lysosomes of Human Polymorphonuclear Leukocytes

Abstract

The enzymatic properties and susceptibility to inhibitors of the chymotrypsin-like neutral protease from human neutrophil granulocytes were investigated. The enzyme hydrolysed several of the most common protease substrates showing highest affinity for casein and highest maximal activity for fibrinogen and denatured Hb. Bovine serum albumin and elastin were not attacked. p-Nitrophenyl esters of methionine, asparagine and isoleucine were hydrolyzed in addition to those of aromatic amino acids. p-Nitroanilides of aromatic amino acids were hydrolyzed very slowly. Both protease and esterase activity were strongly dependent on the ionic strength. The dependence of Km-values of N-substituted phenylalanine p-nitrophenyl esters on the nature of the amino-blocking group suggests the presence of additional substrate binding sites with preference for hydrophobic ligands. The Km and V values for benzyloxycarbonyl-L-phenylalanine-p-nitrophenyl ester were of the same order of magnitude as those of pancreatic chymotrypsin, but protease activity was much lower. An antiserum raised against the purified enzyme gave a single precipitation line with the chymotrypsin-like protease and did not cross react with the elastase-like enzyme.