Effect of rabbit thrombomodulin on thrombin inhibition by antithrombin in the presence of heparin.
Thrombomodulin acts as a cofactor for protein C activation by thrombin (PC activation cofactor activity) and inhibits thrombin-induced fibrinogen clotting (direct anticoagulant activity). In addition, rabbit thrombomodulin has been shown to promote thrombin inactivation by antithrombin (AT-dependent anticoagulant activity). However, a non-acidic form (i.e. non-retarded on ion-exchange chromatography) of thrombomodulin generated by limited proteolysis retained only the PC activation cofactor activity. The acidic form (retarded on ion-exchange chromatography) of thrombomodulin is now shown to prevent the rapid inactivation of thrombin by antithrombin in the presence of heparin, presumably by preventing the formation of the ternary thrombin-AT-heparin complex. This effect was not observed with non-acidic thrombomodulin. When submitted to chondroitinase digestion, thrombomodulin was converted into an essentially non-acidic form that lacked both the AT-dependent and the direct anticoagulant activities but showed a PC activation cofactor function indistinguishable from that of native thrombomodulin. This chondroitinase-digested form did not prevent the catalytic effect of heparin on the inhibition of thrombin by AT. It is concluded that the acidic domain of rabbit thrombomodulin, a chondroitin (dermatan) sulfate glycosaminoglycan, interacts with a site of the thrombin molecule that is not involved in the protein C activation cofactor function, but is essential to the cleavage of fibrinogen or binding of heparin.
Bourin
M C
MC
Department of Veterinary Medical Chemistry, Biomedical Center, Uppsala, Sweden.
D000818:Animals; D000991:Antithrombins / Q000494:pharmacology*; D002810:Chondroitinases and Chondroitin Lyases / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D006493:Heparin / Q000494:pharmacology*; D011486:Protein C / Q000378:metabolism; D011817:Rabbits; D011956:Receptors, Cell Surface / Q000378:metabolism / Q000502:physiology*; D018179:Receptors, Thrombin; D012710:Serum Albumin, Bovine / Q000032:analysis; D013917:Thrombin / Q000037:antagonists & inhibitors*
D000991:Antithrombins; D011486:Protein C; D011956:Receptors, Cell Surface; D018179:Receptors, Thrombin; D012710:Serum Albumin, Bovine; D006493:Heparin; D013917:Thrombin; D002810:Chondroitinases and Chondroitin Lyases