Title: THROMBOMODULIN INHIBITS THE ACTIVATION OF FACTOR XIII BY THROMBIN.
Abstract: The thrombogenic functions of thrombin, studied so far, are diminished or blocked when thrombin is bound to the endothelial cell via its receptor protein thrombomodulin. The thrombomodu-lin-thrombin complex fails to clot fibrinogen, to activate platelet and Factor V, while the activation of the antithrombo-genic protein, protein C is extremely enhanced. Although the activation of Factor XIII (FXIIl) belongs to the thrombogenic functions of thrombin, the effect of thrombomodulin on this process has not been investigated, so far. The aim of this study was to establish whether the presence of thrombomodulin modifies the effect of thrombin on FXIII. The activation was followed by measuring the transglutaminase activity of FXIIIa formed using our UV-kinetic assay (Muszbek et al., Clin. Chem. , 3L, 35, 1985) and by monitoring the amount of activation peptide split off by thrombin from the a subunit. The time dependence of FXIII activation using various thrombin concentrations showed significant difference in the presence and absence of thrombomodulin. Thrombomodulin significantly slowed down the activity of thrombin toward FXIII but did not prevent it completely. The possibility that thrombomodulin influences changes brought about by Ca and noij+the action of thrombin was excluded. When thrombomodulin and Ca were added only after the proteolytic leavage of FXIII had taken place, it had no effect on the Ca induced activation process. The results suggests that thrombomodulin inhibits the rate of conversion of FXIII to its enzymatically active structure but does not influence the amount of FXIIIa formed.
Publication Year: 1987
Publication Date: 1987-01-01
Language: en
Type: article
Indexed In: ['crossref']
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