Studies of the Activation of Human Factor X in Plasma.

Purified human Factor X (FX) was used to develop a new assay and studies were made of the activation of FX initiated by tissue factor (TF) in normal and various deficient plasmas. FX was purified to > 95% homogeneity from commercial FIX concentrates using DEAE-Sephadex, heparin-agarose and preparative polyacrylamide gel electrophoresis. FX (59,000 MW), a glycoprotein, consists of two disulfide linked chains (42,000 and 17,000 MW). The carbohydrate of FX was labeled by a mild oxidation-reduction procedure using periodate and NaB(³H)₄. The specific radioactivity was 1.58 μCi/unit FX with no loss of procoagulant activity . The amount of TCA-soluble ³H-activation peptide released by RVV activation was directly correlated with both FX_a clotting and amidolytic (S-2222) activity. The assay background was much less than 1% of the total radioactivity and the maximum amount of ₃H-peptide released by RVV was 78% of the total radioactivity. In studies of the activation of ³H-FX in normal and various deficient plasmas initiated by various dilutions of TF, there was a significant reduction of FX activation in FVII-, FIX-, and FVIII-deficient plasmas compared to normal or FXI-deficient plasmas. The potential influence of FIX and FVIII on the activation of FX in the presence of dilute TF emphasizes the need to revise current concepts of coagulation pathways and may be related to the abnormalities associated with Hemophilias A and B.