title: The catalysis by heparin of the reaction between thrombin and antithrombin.
abstract: Fluorescence polarization has been used to study the kinetics of the combination of thrombin with antithrombin and its catalysis by the polysaccharide heparin. The heparin-catalysed combination of thrombin and antithrombin is saturable with respect to both thrombin and antithrombin. The rate-determining step of the reaction is approximately 1.7 s-1. The kinetics observed can be explained by proposing that the catalyst of the reaction is not heparin alone but a complex of heparin and antithrombin (bound at the high-affinity site). The temperature dependence of the heparin-catalysed reaction is indistinguishable from that of the uncatalysed reaction. This coincidence is consistent with the rate-limiting step being the same in both cases.
mesh_terms: D000991:Antithrombins / Q000378:metabolism*; D005450:Fluorescamine / Q000378:metabolism; D005454:Fluorescence Polarization; D005456:Fluorescent Dyes / Q000378:metabolism; D006493:Heparin / Q000494:pharmacology*; D007700:Kinetics; D013917:Thrombin / Q000378:metabolism*
chemical_list: D000991:Antithrombins; D005456:Fluorescent Dyes; D005450:Fluorescamine; D006493:Heparin; D013917:Thrombin