title: Functions of the N-terminal domain of secretory leukoprotease inhibitor.
abstract: Secretory leukoprotease inhibitor (SLPI) comprises two homologous domains: the C-terminal domain contains the reactive site, while the function of the N-terminal domain remains unknown. In order to elucidate the function of the N-terminal domain, we studied the kinetics of reactions of human leukocyte elastase with two recombinant forms of SLPI: the full-length inhibitor and the C-terminal domain alone. The reactions of elastase with the full-length inhibitor and the C-terminal domain share the same association rate constant, 2 x 10(6) M-1 s-1, but the complex formed with the C-terminal domain is less stable, with a dissociation rate constant of 8 x 10(-4) s-1, 5 times higher than that of the complex with the full-length inhibitor. The binding of the full-length inhibitor to elastase is greatly accelerated by polyanions. In the presence of submicromolar concentrations (1 microgram/mL) of heparin, the association rate constant is increased by more than 1 order of magnitude. The binding of the C-terminal domain alone to elastase shows much lower sensitivity to heparin; in the presence of 5 microM (25 micrograms/mL) heparin, association of the C-terminal domain with elastase reaches a maximum rate of 7 x 10(6) M-1 s-1, about 3 times higher than the rate in the absence of heparin. Similar differential effects of heparin have been observed on the reactions of alpha-chymotrypsin with the two recombinant forms of SLPI.2=
authors.affiliation: Department of Pathology, State University of New York at Stony Brook 11794.
authors.forename: Q L
authors.initials: QL
authors.lastname: Ying
authors.forename: M
authors.initials: M
authors.lastname: Kemme
authors.forename: S R
authors.initials: SR
authors.lastname: Simon
mesh_terms: D000818:Animals; D002417:Cattle; D002918:Chymotrypsin / Q000037:antagonists & inhibitors; D004795:Enzyme Stability; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D019272:Leukocyte Elastase / Q000037:antagonists & inhibitors / Q000378:metabolism; D007962:Leukocytes / Q000737:chemistry / Q000201:enzymology; D010196:Pancreatic Elastase / Q000037:antagonists & inhibitors / Q000378:metabolism; D053491:Proteinase Inhibitory Proteins, Secretory; D011506:Proteins; D053481:Secretory Leukocyte Peptidase Inhibitor; D015842:Serine Proteinase Inhibitors / Q000737:chemistry* / Q000494:pharmacology / Q000502:physiology
chemical_list: D053491:Proteinase Inhibitory Proteins, Secretory; D011506:Proteins; C506814:SLPI protein, human; D053481:Secretory Leukocyte Peptidase Inhibitor; D015842:Serine Proteinase Inhibitors; D006493:Heparin; D002918:Chymotrypsin; D010196:Pancreatic Elastase; D019272:Leukocyte Elastase