Sialic acid in fibrinogen: effects of sialic acid on fibrinogen-fibrin conversion by thrombin and properties of asialofibrin clot.

The final stage in a series of blood coagulating reactions is fibrinogen-fibrin conversion by thrombin. This reaction consists of fibrinopeptide A and fibrinopeptide B release, polymerization of fibrin monomer, and stabilized fibrin formation by factor XIII. The latter two reactions require calcium. In the present study there was no difference in the rate of thrombin-induced fibrinopeptide release between fibrinogen and asialofibrinogen where sialic acid in the terminal end of carbohydrate moiety of fibrinogen was removed by neuraminidase, but turbidity associated with asialofibrin clot formation was increased more rapidly. In asialo-derivatives, the dissolution time of the clots in high concentrated urea solution tended to be shortened and rigidity as a gel tended to be decreased. In measurement by thromboelastography there was no difference in the reaction time (r) between fibrinogen and asialofibrinogen, but the maximum amplitude (ma) was obviously decreased in asialofibrinogen. Furthermore, when the rate of cross-link formation between gamma chains by F-XIII was compared, the production of gamma-dimer in the same reaction time was found to be lower and formation of stabilized fibrin tended to be retarded in asialofibrinogen. Sialic acid in fibrinogen thus may clearly influence the polymerization of fibrin-monomer and the formation of cross-linked fibrin in a series of reactions for fibrinogen-fibrin conversion. This may be consistent with the theory that fibrinogen sialic acid residues are low affinity calcium-binding sites and influence fibrin assembly.