Summary
In order to investigate the mechanism of thrombin inactivation in the presence of
both antithrombin III (AT III) and α 2-macroglobulin (α 2 M), thrombin and the inhibitors
have been purified from human material and thrombin inactivation studied using purified
reagents either alone or added to defibrinated plasma. Comparison of clotting and
amidolytic activities of residual thrombin allowed to measure the amount of thrombin
bound to α 2 M. In a purified reagent system as well as in plasma, part of exogenous
thrombin is bound to α 2 M. The amount of bound thrombin is related to α 2 M concentration.
Conversely, previous plasma α 2 M depletion by immunoabsorption increases the consumption
of heparin-cofactor activity by exogenous thrombin. Thus AT III and α 2 M compete
for thrombin inactivation. This finding could be of practical interest in clinical
situations associating high plasma α 2 M levels and a decrease of AT III concentration.
Keywords
Antithrombin III-α 2 macroglobulin-Thrombin
