Tryptase from rat mast cells converts bovine prothrombin to thrombin.

The effect of tryptase purified from rat peritoneal mast cells on bovine prothrombin was examined. Tryptase activated prothrombin, as evidenced by the increase in thrombin activity with a synthetic substrate, t-butyloxy-carbonyl-Val-Pro-Arg-4-methylcoumaryl-7-amide. The apparent Km value toward bovine prothrombin and the kcat value were 2.3 microM and 46.3 s-1, respectively. Studies on the time course of prothrombin activation by tryptase and by activated factor X (Xa), and analysis of the activation products on sodium dodecyl sulfate gel electrophoresis showed that the process of activation of prothrombin by tryptase was similar to that by Xa except that an intermediate of 67,000 daltons was formed.