Characterization of the binding of human tissue-type plasminogen activator to platelets

D. E. Vaughan, M. E. Mendelsohn, P. J. Declerck, E. Van Houtte, D. Collen, J. Loscalzo

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42 Scopus citations

Abstract

Cell surface binding sites for the constituent proteins of the fibrinolytic system may play a role in the localization and regulation of fibrinolysis. In the present study, specific binding of recombinant human tissue-type plasminogen activator (rt-PA) to human blood platelets was identified and characterized. 125I-labeled rt-PA was found to bind specifically, saturably, and reversibly to the surface of gel-filtered platelets, reaching equilibrium within 5 min at 22°C. Scatchard analysis revealed a single class of binding sites. Unstimulated platelets bound 120,000 ± 24,000 (mean ± S.D.) molecules/platelet with an apparent K(d) of 340 ± 25 nM, whereas thrombin-stimulated platelets bound 290,000 ± 32,000, molecules/platelet with an apparent K(d) of 800 ± 60 mM. Binding of 0.1 μM 125I-rt-PA was > 90% reversible by a 50-fold excess of unlabeled rt-PA. Binding was not inhibited by fibrinogen or single chain urokinase-type plasminogen activator, but plasminogen partially competed for binding of 125I-rt-PA to platelets (up to 40% displacement). These findings indicate that the platelet surface possesses a large number of specific, low affinity binding sites for t-PA and provide further evidence for the role of platelets in localization and regulation of fibrinolysis.

Original languageEnglish (US)
Pages (from-to)15869-15874
Number of pages6
JournalJournal of Biological Chemistry
Volume264
Issue number27
StatePublished - 1989

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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