Kinetic study on the initial stage of the fibrinogen-fibrin conversion by thrombin. (III) Effects of competitive inhibitors.

By using the turbidimetrical procedure, the inhibition constants, Kip, of competitive inhibitors of thrombin were estimated in systems of fibrinogen-thrombin-inhibitor. In the presence of a competitive inhibitor such as benzamidine, p-aminobenzamidine, tosylarginine methyl ester, MD-805, and antithrombin III-heparin, the turbidity change of reaction mixture was traced on the initial stage of the fibrinogen-fibrin conversion catalyzed by thrombin. The formation rate of the smallest polymer as detectable by turbidimetry was measured from evaluating the induction period of turbidity-time curves. The Kip values thus obtained were a little less than or agreed well with the inhibition constants, Ki, reported on systems of synthetic substrate-thrombin-inhibitor.