Summary
The effects of pH, salt and amino acid (β-alanine) concentration on the rate of thrombin
formation and antithrombin activity in recalcified plasma was studied from the viewpoint
of reaction rate kinetics, and units of thrombin and antithrombin activity defined
on this basis. Optimal thrombin activity (fibrin formation) was observed between pH
6.5 and 8.0 and at 0.19 M NaCl. Maximal antithrombin activity occurred at pH 8.5 and
0.10 M sodium chloride.
Antithrombin activity, examined under optimal conditions as well as under the influence
of changes in pH, and of salt and amino acid concentrations proved to follow first-order
reaction kinetics. The activities of thrombin and antithrombin changed in a diphasic
manner with increasing concentrations of salt or amino acid and such change may represent
subtle protein-protein or protein-salt interactions.
The antithrombin activity of fifteen normal plasmas was determined from reaction rate
studies of thrombin destroyed during recalcification of human plasma and compared
to the inactivation of bovine thrombin by citrated plasma.
A concept of “coagulability” of plasma based on the measurement of two independent
parameters, fibrinogen and antithrombin, and their kinetic interrelationships, was
developed as an approach to a functional concept of hemostasis.
