title: The inhibition of human factor Xa by plasminogen activator inhibitor type 1 in the presence of calcium ion, and its enhancement by heparin and vitronectin.
abstract: Plasminogen activator inhibitor type 1 (PAI-1), a member of serine proteinase inhibitor superfamily, is known to inhibit thrombin in the presence of either heparin or vitronectin. We analyzed possible inhibitory activity of PAI-1 on human factor Xa. PAI-1 inhibited factor Xa in the presence of calcium ion (Ca2+), whereas no inhibition was observed in the absence of Ca2+. Half maximal enhancement by Ca2+ was obtained at 0.8 mM. An equimolar complex formation between factor Xa and PAI-1 in the presence of Ca2+ was observed by SDS polyacrylamide gel electrophoresis. Both unfractionated heparin and vitronectin enhanced the inhibition only in the presence of Ca2+. Apparent second-order rate constant (ki) for the inhibition of factor Xa by PAI-1 at 5 mM Ca2+ was 1.6 x 10(4) M-1 s-1, and was enhanced 3-fold by 2 u/ml of heparin (4.6 x 10(4) M-1 s-1) and 10-fold by 100 nM vitronectin (1.6 x 10(5) M-1 s-1), respectively. The interaction between Ca(2+)-bound factor Xa and PAI-1 could be important from the view of PAI-1 neutralization and enhancement of fibrinolysis.
authors.affiliation: Department of Physiology, Hamamatsu University School of Medicine, Shizuoka, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Urano
authors.forename: H
authors.initials: H
authors.lastname: Ihara
authors.forename: Y
authors.initials: Y
authors.lastname: Takada
authors.forename: N
authors.initials: N
authors.lastname: Nagai
authors.forename: A
authors.initials: A
authors.lastname: Takada
mesh_terms: D002118:Calcium / Q000494:pharmacology*; D004591:Electrophoresis, Polyacrylamide Gel; D005172:Factor XI / Q000037:antagonists & inhibitors*; D006031:Glycosylation; D006493:Heparin / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D008970:Molecular Weight; D017395:Plasminogen Activator Inhibitor 1 / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000494:pharmacology; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology*; D013917:Thrombin / Q000494:pharmacology; D019096:Vitronectin / Q000494:pharmacology*
chemical_list: D017395:Plasminogen Activator Inhibitor 1; D011994:Recombinant Proteins; D015842:Serine Proteinase Inhibitors; D019096:Vitronectin; D006493:Heparin; D005172:Factor XI; D013917:Thrombin; D002118:Calcium