Year: 1981
Type: conference-paper
Abstract: The rates of thrombin inactivation by AT III were studied by stopped-flow fluorimetry using p-aminobenzami- dine as an active site probe. p-Aminobenzamidine binds to thrombin with a of KD of 35 μM and a 50-fold fluorescence enhancement. The bimolecular rate constant for the thrombin-AT III reaction was 8.7 × 103 M-1 s-1 at 25° C and pH 7.4, with no diminished amplitude or evidence for a limiting rate at AT III concentrations as high as 10-4 M. Using lower AT III concentrations, an identical bimolecular rate constant was obtained by discontinuous assay of residual thrombin activity. Inactivation of thrombin by antithrombin III complexed with stoichiometric high affinity heparin at concentrations between 2.5 to 20 μM resulted in biphasic reactions: a rapid phase complete in less than 10 milliseconds and a slow phase with a rate constant of 4-6 s-1 . Relative amplitudes and slow phase rate constants showed slight changes over this AT III-heparin concentration range. These results are consistent with weak initial binding of AT III to thrombin in the absence of heparin (KD> 10-4 M), with a major part of the heparin rate enhancement due to a substantial decrease in the KD for the initial binding step. Supported by Michigan Heart Association and USPHS grant F32 HL06171-01.
Source: Thrombosis and Haemostasis
Authors: S T Olson, S A Evans, J D Shore
Institution: Henry Ford Hospital
Language: English
Subfield: Hematology
Field: Medicine
Domain: Health Sciences
Open Access status: bronze
OpenAlex ID: W2883708179