Acid-stable low molecular mass proteinase inhibitors in human lung lavage

An acid-stable, low molecular mass proteinase inhibitor, bronchial mucus proteinase inhibitor (BMPI), has been isolated from sputum and partially characterised. A single band with a modal molecular mass of 18 700 was observed following SDS-polyacrylamide gel electrophoresis. BMPI inhibited human leukocyte elastase, cathepsin G, trypsin and chymotrypsin, but not porcine pancreatic elastase. Although BMPI had a molecular mass close to the similarly isolated inhibitor of Girard et al. (Girard, F., Tournier, J.M., Polu, J.M. & Sadoul, P. (1980), Bull. Eur. Physiopathol. Respir. 16 (Suppl.) 237-245), and although it showed immunological cross reactivity to the low molecular mass inhibitor of Kramps et al. (Kramps, J.A., Franken, C., Meyer, C.J.L.M. & Dijkman, J.H. (1981) J. Histochem. Cytochem. 29, 712-719), it was found to have an amino-acid profile different to any previously described inhibitor. BMPI was detectable in bronchoalveolar lavage fluid collected from healthy and diseased human lungs. The median molar ratio of BMPI/alpha 1-proteinase inhibitor (alpha 1 PI) observed in these lavage samples was 0.7, which is generally higher than those derived from the data of other authors. This suggests that BMPI is a different protein to those previously described, although its exact relationship to other low molecular mass proteinase inhibitors remains to be determined.