title: Inhibition of neutrophil cathepsin G by oxidized mucus proteinase inhibitor. Effect of heparin.
abstract: Oxidation of mucus proteinase inhibitor (MPI) transforms Met73, the P'1 residue of its active center into methionine sulfoxide and lowers its affinity for neutrophil elastase [Boudier, C., and Bieth, J. G. (1994) Biochem. J. 303, 61-68]. Here, we show that the oxidized inhibitor has also a decreased affinity for neutrophil cathepsin G and pancreatic chymotrypsin. The Ki of the oxidized MPI-cathepsin G complex (1.2 microM) is probably too high to be compatible with significant inhibition of cathepsin G in inflammatory lung secretions. Stopped-flow kinetics shows that, within the inhibitor concentration range used, the mechanism of inhibition of cathepsin G and chymotrypsin by oxidized MPI is consistent with a one-step reaction, [equation in text] whereas the inhibition of elastase takes place in two steps, [equation in text]. Heparin, which accelerates the inhibition of the three proteinases by native MPI, also favors their interaction with oxidized MPI. Flow calorimetry shows that heparin binds oxidized MPI with Kd, Delta H degrees, and Delta S degrees values close to those reported for native MPI. In the presence of heparin, oxidized MPI inhibits cathepsin G via a two-step reaction characterized by Ki = 0.22 microM, k2 = 0.1 s-1, k-2 = 0.023 s-1, and Ki = 42 nM. Under these conditions, in vivo inhibition of cathepsin G is again possible. Heparin also improves the inhibition of chymotrypsin and elastase by oxidized MPI by increasing their kass or k2/Ki and decreasing their Ki. Our data suggest that oxidation of MPI during chronic bronchitis may lead to cathepsin G-mediated lung tissue degradation and that heparin may be a useful adjuvant of MPI-based therapy of acute lung inflammation in cystic fibrosis.
authors.affiliation: Laboratoire d'Enzymologie, INSERM U 392, Université Louis Pasteur de Strasbourg, France.
authors.forename: C
authors.initials: C
authors.lastname: Boudier
authors.forename: M
authors.initials: M
authors.lastname: Cadène
authors.forename: J G
authors.initials: JG
authors.lastname: Bieth
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D056649:Cathepsin G; D002403:Cathepsins / Q000037:antagonists & inhibitors*; D002417:Cattle; D002918:Chymotrypsin / Q000037:antagonists & inhibitors; D006493:Heparin / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D009504:Neutrophils / Q000187:drug effects / Q000201:enzymology*; D010084:Oxidation-Reduction; D010196:Pancreatic Elastase / Q000037:antagonists & inhibitors; D053491:Proteinase Inhibitory Proteins, Secretory; D011506:Proteins / Q000378:metabolism / Q000494:pharmacology*; D012697:Serine Endopeptidases; D015842:Serine Proteinase Inhibitors / Q000378:metabolism / Q000494:pharmacology
chemical_list: D053491:Proteinase Inhibitory Proteins, Secretory; D011506:Proteins; D015842:Serine Proteinase Inhibitors; D006493:Heparin; D002403:Cathepsins; D012697:Serine Endopeptidases; D002918:Chymotrypsin; C534094:CTSG protein, human; D056649:Cathepsin G; D010196:Pancreatic Elastase