Clotting of bovine fibrinogen by liver transamidase.

C ASEIN, IN CONJUNCTION W ITH LABELED GLYCINE ETHYL ESTER, proved to be a suitable material in the study of liver transglutaminase.1 The liver enzyme catalyzes the incorporation of the labeled amine into the glutamine residues of the casein and thus can easily be followed in a scintillation counter. Since transglutaminase catalyzes the cross-bonding of the fibrin clot,2 we explored the possibility of using fibrinogen instead of casein for the study of transglutaminase. In the course of these studies, we observed that after an initial incorporation of glycine ethyl ester into fibrinogen, it began to lose the labeled amine, and in the same time the reaction mixture developed turbidity, indicating that the enzyme catalyzed the cross-bonding of fibrinogen molecules. The experiments in this paper show that indeed the liver transglutaminase connects fibrinogen molecules into an urea insoluble clot.