The suicide substrate reaction between plasminogen activator inhibitor 1 and thrombin is regulated by the cofactors vitronectin and heparin

• Published in: Blood Vol. 90; no. 5; pp. 1874 - 1882
• Main Authors: VAN MEIJER, M, SMILDE, A, TANS, G, NESHEIM, M. E, PANNEKOEK, H, HORREVOETS, A. J. G
• Format: Journal Article
• Language: English
• Published: Washington, DC The Americain Society of Hematology 01.09.1997
• Subjects: Animals; Biological and medical sciences; Blood coagulation. Blood cells; Fundamental and applied biological sciences. Psychology; General aspects, investigation methods, hemostasis, fibrinolysis; Heparin - metabolism; Heparin - pharmacology; Humans; Molecular and cellular biology; Plasminogen Activator Inhibitor 1 - metabolism; Substrate Specificity - drug effects; Swine; Thrombin - metabolism; Vitronectin - metabolism; Vitronectin - pharmacology; Human; Serine endopeptidases; Enzyme; Interaction; Thrombin; Vitronectin; Anticoagulant; Cofactor; Fibrinolysis; Substrate; Peptidases; Plasminogen activator inhibitor 1; Regulation(control); Endogenous; Hydrolases; Glycosaminoglycan; Kinetics; Heparin
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.v90.5.1874

The interaction of thrombin with plasminogen activator inhibitor 1 (PAI-1) is shown to result in the simultaneous formation of both cleaved PAI-1 and a sodium dodecyl sulfate-stable thrombin-PAI-1 complex. The kinetics of this reaction can be described by a "suicide substrate" mechanism that includes a branched reaction pathway, which terminates in either the stable inhibitor-enzyme complex or the cleaved inhibitor plus free enzyme. Because of the branched pathway, approximately three moles of PAI-1 are needed to completely inhibit one mole of thrombin. Heparin and vitronectin enhance the rate of inhibition from 9.8 x 10(2) L mol(-1) s(-1) to 6.2 x 10(4) L mol(-1) s(-1) and 2.1 x 10(5) L mol(-1) s(-1), respectively, under optimal conditions. In addition to enhancing the rate of inhibition, both cofactors increase the apparent stoichiometry of the PAI-1-thrombin interaction, with cofactor concentration dependencies similar to the inhibition reaction. Thus, at 37 degrees C approximately six cleavage reactions occur per inhibition reaction. Therefore, thrombin will efficiently inactivate PAI-1 in the presence of either vitronectin or heparin, unless a sufficient excess of the inhibitor is present. These results show that physiological cofactors are able to switch a protease-serpin inhibition reaction to a substrate reaction, depending on the local concentrations of each of the components.