The transglutaminase in vascular cells and tissues could provide an alternate pathway for fibrin stabilization.

A thrombin-independent transglutaminase (TG) has been identified in vascular cells and tissues from human, rabbit, rat, porcine, and bovine sources. The vascular TG had several properties that were similar but not identical to guinea pig liver TG. Both enzymes had similar chromatographic and electrophoretic properties, preferentially cross-linked the alpha-chains of fibrinogen, and reacted with polyclonal and monoclonal anti-guinea-pig liver TG antibodies. However, the TG from adult bovine aortic endothelial (ABAE) cells exhibited a novel Ca2+/Mg2+ dependence for enzymatic activity that was distinct from that of purified guinea pig liver TG. The mol wt of the vascular TG (79 +/- 3 kd) determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was slightly lower than the purified guinea pig liver TG (85 +/- 9 kd). The TG antigen was detected by immunohistochemical techniques in association with the endothelial and smooth muscle cells of arteries, veins, venules, and capillaries. The TG antigen also codistributed with the fibronectin antigen along the hepatic sinusoids. The ABAE cell TG cross-linked alpha 2-plasmin inhibitor to fibrinogen and caused the modified fibrinogen to be 40-fold more resistant to plasminolysis. A thrombin-independent TG in vascular cells of blood vessels could provide an alternate pathway to inhibit fibrinolysis and promote fibrin stabilization.