[Activation of factor XIII by beta-thrombin]

It was found that similar to alpha-thrombin, beta-thrombin (possessing a high esterase and only a trace coagulating activities) converts plasmic transglutaminase (factor XIII) into its active form, thus promoting stabilization of fibrin. Activation of pure and plasmic preparations of factor XIII after incubation with beta-thrombin was observed in vitro. alpha-Thrombin at concentration corresponding to the trace coagulating activity of beta-thrombin had no activating effects. An intravenous injection of beta-thrombin to animals with aminazine-inhibited anticoagulating system reflectory arc resulted in an increase of factor XIII activity in the same way as was observed in vitro. On the other hand, an intravenous injection of beta-thrombin to intact animals did not increase factor XIII activity, which may be accounted for by a decrease in the level of factor XIII due to activation of the anticoagulating system.