Blood clotting factor IX Kashihara: amino acid substitution of valine-182 by phenylalanine

Hemophilia B Kashihara is a severe hemorrhagic disorder in which the factor IX antigen is present in normal amounts but factor IX biological activity is markedly reduced. In addition, purified factor IX Kashihara is not activated by purified factor XIa in the presence of calcium ions. Amino acid sequence analysis of one of the tryptic peptides isolated from factor IX Kashihara indicated that Val-182 (equivalent to Val-17 in the chymotrypsin numbering system) had been replaced by Phe. No substitution was found in the members of the catalytic triad His-221, Asp-269, and Ser-365 of factor IX Kashihara. The Val-to-Phe replacement found in factor IX Kashihara appears to sterically hinder the cleavage of Arg 180-Val 181 by factor XIa required for the activation of this zymogen.     

Blood clotting factor IX Niigata: substitution of alanine-390 by valine in the catalytic domain

Factor IX Niigata is a mutant factor IX responsible for the moderately severe hemophilia B in a patient who has a normal level of factor IX antigen with reduced clotting activity (1-4% of normal). We reported previously that the purified mutant protein could be converted to the factor IXa beta form by factor XIa/Ca2+ at a rate similar to that in the case of normal factor IX, but the resulting mutant factor IXa beta could not activate factor X in the presence of factor VIII, Ca2+, and phospholipids (Yoshioka, A. et al. (1986) Thromb. Res. 42, 595-604). In the present study, we analyzed factor IX Niigata at the structural level to elucidate the molecular abnormality responsible for the loss of clotting activity. Amino acid sequence analysis of a peptide obtained on lysyl endopeptidase digestion, coupled with subsequent SP-V8 digestion, demonstrated that the alanine at position 390 was substituted by valine in the catalytic domain of the factor IX Niigata molecule.     

Blood clotting factor IX. Loss of activity after cleavage of sialic acid residues

Enzymatic cleavage of sialic acid from human blood clotting factor IX results in a loss of factor IX clotting activity. The loss of clotting activity and the rate of release of sialic acid follow the same time courses. Control experiments have ruled out several explanations for the loss of factor IX activity: proteolytic degradation, inhibitory effects of free sialic acid, and non-specific inhibition of the clotting assays. Furthermore, no inhibition was seen when similar enzymatic cleavage was carried out on factor X and factor VIII. Therefore, we suggest that the loss of factor IX activity is the direct result of cleavage of sialic acid from the protein. Most of the inhibition appeared to be an effect on the activity of factor IXa itself, and thus far, little or no effect has been shown on the activation of factor IX to IXa. The structural basis for this unusual effect of sialic acid on protein function currently is being investigated.     

Counteracting clotting in sepsis

The complexity of factors that regulate bleeding and coagulation has long confounded researchers. Andrew Wei and Shaun Jackson help clear the air by examining clinical findings pointing to a mechanistic basis for a common bleeding disorder, immune thrombocytopenic purpura. Mark Kahn tackles two research studies that could lead to improved therapies for a coagulation syndrome that hits people with severe sepsis.     

Blood clotting and coagulation factors: the work of Yale Nemerson. 1980, 1982

After developing a blood disorder, Yale Nemerson became interested in hematology. This led to his lifelong study of thrombogenic tissue factor and to his contributions to developing the modern theory of blood coagulation. The two Classic papers reprinted here detail some of Nemerson's studies on coagulation factors IX and VII.