Kinetic studies of the activation of factor X by factors IXa and VIII:C in the absence of thrombin.

The activation of factor X by the components of the intrinsic coagulation pathway has been studied using a preparation of bovine factor VIII which did not require 'activation' with thrombin prior to its participation in the reaction. Measurements of the kinetic parameters indicated that factor VIII:C stimulated the formation of factor Xa via a 170-fold increase in the Vmax; factor VIII:C had little effect on the Km for factor X.