[Factor XIII as a stimulator of thrombin activity].

The coagulating activity of thrombin was increased by 120% and the esterase activity--by 100% after incubation of thrombin with factor XIII. Factor XIII also stimulated generation of thrombin in the test of two-step estimation of prothrombin. The effect, arising from the interaction of factor XIII with thrombin, was specific for this enzyme because the esterase activity of trypsin was not increased during incubation of enzyme with factor XIII under the same conditions. The data obtained suggest that factor XIII or its fragment are effectors of enzymatic activity of thrombin in vitro and in vivo.