Enhanced Affinity of Fibrinogen and Factor XIII Induced by Limited Proteolysis
Previous studies have shown that tissue transglutaminase has strong affinity for fibrinogen. In this study, the binding of protransglutaminase, i.e., plasma Factor XIII(a2b2) and platelet Factor XIII (a2), to fibrinogen was examined by ultracentrifugation, exclusion and affinity chromatography, Immunoelectrophoresis, and salt precipitation. Affinity was detected only by salting out and affinity chromatography. Limited proteolysis to form Factor XIIIa (a′2b2 and a′2) enhanced the affinity for fibrinogen. Limited proteolysis of fibrinogen by thrombin or ancrod enhanced affinity for both a2b2 and a2. Fibrin also bound a′2b2 and a′2. The b2 subunit exhibited no affinity for fibrinogen or fibrin. Thus, in the presence of fibrin(ogen), a′2b2 gave rise to a fibrin(ogen)-a′2 complex, and the b2 subunit was liberated.The enhanced affinity for fibrinogen induced by limited proteolysis of Factor XIII suggests that fibrinogen could serve to adsorb active transglutaminase(s) released or generated in the circulation.