Inhibition of proteinase 3 by [alpha]1-antitrypsin in vitro predicts very fast inhibition in vivo.
Neutrophil proteinase 3 (Pr3) cleaves elastin and other matrix proteins, and is thought to cause lung tissue destruction in emphysema and cystic fibrosis. Its deleterious action is theoretically prevented by alpha1-antitrypsin, a serpin present in lung secretions. We have evaluated the anti-Pr3 activity of this inhibitor to decide whether it may play a physiologic proteolysis-preventing function in vivo. We show that (i). the oxidized inhibitor does not inhibit Pr3; (ii). the inhibitor competes favorably with elastin for the binding of Pr3, but is less efficient for inhibiting elastin-bound proteinase than for complexing free enzyme; and (iii). the inhibition takes place in at least two steps: the enzyme and the inhibitor first form a high-affinity reversible inhibitory complex EI* with an equilibrium dissociation constant K*i of 38 nM; EI* subsequently transforms into an irreversible complex EI with a first-order rate constant k2 of 0.04 s-1. Because the alpha1-antitrypsin concentration in the epithelial lining fluid is much higher than K*i, any Pr3 molecule released from neutrophils will be taken up as an EI* complex within much less than 1 s, indicating very efficient inhibition in vivo.
Duranton
Jérôme
J
Laboratoire d"Enzymologie, INSERM U 392, Universitĕ Louis Pasteur de Strasbourg, Illkirch, France.
Bieth
Joseph G
JG
D004549:Elastin / Q000378:metabolism; D007700:Kinetics; D053146:Myeloblastin; D010084:Oxidation-Reduction; D011237:Predictive Value of Tests; D012697:Serine Endopeptidases / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D015842:Serine Proteinase Inhibitors / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D000515:alpha 1-Antitrypsin / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*
D015842:Serine Proteinase Inhibitors; D000515:alpha 1-Antitrypsin; D004549:Elastin; D012697:Serine Endopeptidases; D053146:Myeloblastin