Human bronchial leucocyte proteinase inhibitor. Rapid isolation and kinetic analysis with human leucocyte proteinases

Abstract

Bronchial leukocyte proteinase inhibitor (BLPI) is an 11,000 MW protein found in human mucous secretions. This inhibitor apparently controls the serine proteinases, elastase and cathepsin G, released from extravascular polymorphonuclear leukocytes. A simple, single-step chromatographic procedure for the isolation of BLPI was developed based on its affinity for chymotrypsin. The purified inhibitor was homogeneous by electrophoresis and gel filtration. Amino acid analyses were in close agreement with previous reports; they showed BLPI to be rich in proline and cystine, but lacking in histidine. The role of BLPI, with respect to human leukocyte elastase and cathepsin G, was further studied by close examination of the kinetic parameters. The kinetics of association (kon) and dissociation (koff) for BLPI were determined with bovine trypsin and chymotrypsin. Equilibrium dissociation constants (Ki) of 1.87 .times. 10-10M, 4.18 .times. 10-9 M, 8.28 .times. 10-9 M and 2.63 .times. 10-8 M were obtained for human leukocyte elastase, cathepsin G, bovine trypsin and chymotrypsin, respectively. These results are discussed with respect to BLPI''s possible function in vivo and to its role relative to other inhibitors in bronchial secretions.