Interaction of S-protein of complement with thrombin and antithrombin III during coagulation. Protection of thrombin by S-protein from antithrombin III inactivation

E. R. Podack, B. Dahlback, J. H. Griffin

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S-protein, the inhibitor in plasma of the membrane attack complex of complement, appears to have a second function in coagulation. S-protein during clotting enters into a trimolecular complex with thrombin and antithrombin III (ATIII). Functionally, S-protein in the presence of low concentrations of heparin, protects thrombin from inactivation by ATIII. Complex formation between S-protein and thrombin, and between S-protein, thrombin, and ATIII, was demonstrated by agarose gel electrophoresis and by two-dimensional immunoelectrophoresis of purified proteins and in recalcified, clotted plasma. Formation of the trimolecular S-thrombin-ATIII complex was strictly dependent on the presence of thrombin. No association was detectable between S-protein and ATIII or between S-protein and prothrombin. Heparin was not required for the formation of the bimolecular S-protein-thrombin complex or the trimolecular S-protein-ATIII complex. The protective effect of S-protein on inactivation of thrombin by ATIII was demonstrated in functional assays with purified proteins and in plasma only in the presence of low concentrations of heparin. Thus, S-protein may mediate its effect by scavenging heparin required for ATIII activation. It is suggested that the protection of thrombin by S-protein from inactivation by ATIII may be of physiological importance.

Original languageEnglish (US)
Pages (from-to)7387-7392
Number of pages6
JournalJournal of Biological Chemistry
Issue number16
StatePublished - Dec 1 1986


ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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