Abstract
Factor IX and factor X have sialic acid in O-linked and N-linked oligosaccharides on their activation peptides, and a terminal sialic acid is found on a recently described O-linked tetrasaccharide at Ser-61 in the light chain of human factor IXa. In studies presented here, the potential role of sialic acid residues in mediating activity of human coagulation factors IX and X was tested after enzymatic removal of sialic acid residues. In contrast to previous reports, treatment of factor IX or factor IXa with recombinant sialidase did not decrease the rate of factor IX activation or proteolytic properties of human factor IXa. The activation rates of factor IX and desialated factor IX were indistinguishable when treated with factor XIa, with factor VIIa/tissue factor complex, and with the factor X activating enzyme from Russell's viper venom. Desialated human factor IXa showed full activity in the non-activated partial thromboplastin time assay and retained full "tenase" activity in a coupled amidolytic assay. Similar experiments with human factor X showed no detectable loss of clotting activity in the prothrombin time assay after desialation. Additionally, desialated human factor X was cleaved by the factor X activating enzyme from Russell's viper venom and intrinsic tenase at the same rate as untreated factor X when analyzed by SDS-polyacrylamide gel electrophoresis. These studies have shown that factor IX and factor X clotting activity are not dependent on sialic acid content. Further studies are needed to determine whether desialated factor IX binds to endothelial cells, and whether factors IX and X are more rapidly cleared from circulation or have altered susceptibility to proteolysis after enzymatic removal of sialic acid.
Highlights
Human coagulation factor IX is a vitamin K-dependent coagulation factor which is essential for normal hemostasis (1)
The proposed consensus sequence (Cys-X-X-Gly-Gly-Thr/Ser-Cys) for incorporation of fucosyl modifications in epidermal growth factor (EGF) domains is found in human factor IX, t-PA, urokinase, factor VII, and factor XlI but not in factor X or bovine factor IX (7)
Enzymatic removal of sialic acid has been reported to result in the loss of factor IX clotting activity without affecting the rate at which factor IX is cleaved by the factor X activating enzyme from Russell's viper venom (RW-X) (8)
Summary
Vol 270, No 12, Issue of March 24, pp. 6537-6542, 1995 Printed in U.S.A. Enzymatic Removal of Sialic Acid from Human Factor IX and Factor X Has No Effect on Their Coagulant Activity*. Desialated human factor X was cleaved by the factor X activating enzyme from Russell's viper venom and intrinsic tenase at the same rate as untreated factor X when analyzed by SDS-polyacrylamide gel electrophoresis These studies have shown that factor IX and factor X clotting activity are not dependent on sialic acid content. The costs of publication of this article were defrayed in part by the payment of page charges. Enzymatic removal of sialic acid has been reported to result in the loss of factor IX clotting activity without affecting the rate at which factor IX is cleaved by the factor X activating enzyme from Russell's viper venom (RW-X) (8). Factor X, which lacks the consensus site for a fucose-linked oligosaccharide in its light chain, did not lose clotting activity following enzymatic removal of sialic acid (8). Desialated factor IX, IXa, and X were found to retain full enzymatic activity in plasma and purified systems
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