title: The proteinase: mucus proteinase inhibitor binding stoichiometry.
abstract: In the nanomolar enzyme and inhibitor concentration range, 1 mol of mucus proteinase inhibitor (MPI) inhibits 1 mol of neutrophil elastase, cathepsin G, trypsin, and chymotrypsin. In the micromolar concentration range, the enzyme:inhibitor binding stoichiometry is still 1:1 for elastase but shifts to 2:1 for the three other proteinases. These data could be confirmed by three nonenzymatic methods: (i) fluorescence anisotropy measurements of mixtures of proteinases with 5-dimethylaminonaphthalene-1-sulfonylated or fluoresceinylated MPI, (ii) absorption spectrocospy of fluorescein-MPI-proteinase complexes isolated by gel filtration, (iii) analytical ultracentrifugation which showed that the molecular mass of the MPI-chymotrypsin complex is 56 kDa, whereas that of the MPI-elastase complex is 39 kDa. The binary MPI-elastase complex is unable to inhibit trypsin or cathepsin G. On the other hand, 1 mol of elastase displaces 2 mol of trypsin or cathepsin G from their ternary complexes with MPI.
authors.affiliation: Laboratoire d'Enzymologie, Institut National de la Santé et de la Recherche Médicale Unité 237, Université Louis Pasteur de Strasbourg, Illkirch, France.
authors.forename: C
authors.initials: C
authors.lastname: Boudier
authors.forename: J G
authors.initials: JG
authors.lastname: Bieth
mesh_terms: D000818:Animals; D001665:Binding Sites; D056649:Cathepsin G; D002403:Cathepsins / Q000378:metabolism; D002417:Cattle; D002918:Chymotrypsin / Q000378:metabolism; D016650:Fluorescein-5-isothiocyanate; D005454:Fluorescence Polarization; D007700:Kinetics; D019272:Leukocyte Elastase; D009093:Mucus / Q000201:enzymology*; D010196:Pancreatic Elastase / Q000378:metabolism; D011480:Protease Inhibitors / Q000378:metabolism*; D012697:Serine Endopeptidases; D014357:Trypsin / Q000378:metabolism; D014461:Ultracentrifugation; D000515:alpha 1-Antitrypsin / Q000378:metabolism
chemical_list: D011480:Protease Inhibitors; D000515:alpha 1-Antitrypsin; D002403:Cathepsins; D012697:Serine Endopeptidases; D002918:Chymotrypsin; D056649:Cathepsin G; D010196:Pancreatic Elastase; D019272:Leukocyte Elastase; D014357:Trypsin; D016650:Fluorescein-5-isothiocyanate