Two proteolytic enzymes, a cathepsin B-like activity and prolyl endopeptidase activity, were demonstrated in cellular elements and fluids obtained from human bronchopulmonary washings and in fragments of human lung tissue. Model synthetic substrates were used for the determination of enzyme activities. Cathepsin B-like activity was determined with N-benzyloxycarbonyl-L-leucyl-L-leucyl-L-arginyl-2-naphthylamide. The rate of reaction with this substrate was 300 times greater than the rate with alpha-N-benzoyl-DL-arginyl-2-naphthylamide, a substrate commonly used for the determination of cathepsin B activity. Prolyl endopeptidase was determined with N-benzyloxycarbonyl-glycyl-L-prolyl-sulfamethoxazole as the substrate. The two model substrates make possible the determination of enzyme activities in as little as 10 to 50 microliters of lavage fluid. High cathepsin B-like activity and prolyl endopeptidase were generally associated with high macrophage counts in lavage fluids. This observation and the findings that cathepsin B activity is more than 4.5 times higher in normal monocytes than in neutrophils and that prolyl endopeptidase activity could not be detected in normal neutrophils suggest that the enzymes in lavage fluids are mainly derived from macrophages. Large differences in cathepsin B-like activity in certain lavage fluids containing similar macrophage counts suggest the possibility of enzyme induction in these cells. High cathepsin B-like activity and prolyl endopeptidase were also found in lavage fluids after removal of cells by centrifugation. The possibility that these enzymes affect collagen turnover and lung remodeling needs to be explored.
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