The preparation of activated factor X and its action on prothrombin.

The preparation of activated Factor X from reaction mixtures of bovine Factor X and Russell's-viper venom is described. The molecular weight of purified protein varies about a mean value of 40000; this variation is the result of at least two forms of Factor Xa. The action of activated Factor X, together with purified Factor V, was studied on purified prothrombin and the reaction products were isolated. In addition to thrombin, two other polypeptides with molecular weights of 16000 and 19500 were recovered.