title: Interaction of factor XIa and antithrombin in the presence and absence of heparin.
abstract: We have studied the interaction between purified human factor XIa and antithrombin in the presence and absence of well-characterized preparations of heparin. The concentrations of hemostatic enzyme, protease inhibitor, and mucopolysaccharide were 5.76 X 10(-8) mol/L, 5.76 X 10(6) mol/L, and either 5.88 X 10(6) mol/L or 0, respectively. Kinetic investigation of this process using a tritiated factor IX substrate demonstrated that the pseudo first-order rate constants of this reaction in the presence and absence of heparin are approximately 1.0 min-1 and approximately 0.025 min-1, respectively. Thus, the rate of hemostatic enzyme-protease inhibitor complex formation is accelerated by about 40-fold in the presence of saturating levels of the mucopolysaccharide. These results were confirmed in a qualitative manner by directly monitoring the generation of factor XIa-antithrombin interaction product with sodium dodecyl sulfatepolyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analysis using an antibody population specific for the protease inhibitor.
mesh_terms: D000991:Antithrombins / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005172:Factor XI / Q000378:metabolism*; D015945:Factor XIa; D006493:Heparin / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D011480:Protease Inhibitors / Q000494:pharmacology
chemical_list: D000991:Antithrombins; D011480:Protease Inhibitors; D006493:Heparin; D005172:Factor XI; D015945:Factor XIa