A Normal Inhibitor of the Blood Coagulation Contact Reaction Product

A method is described for studying and measuring the activity of a normally occurring inhibitor of the blood coagulation contact reaction product (activated PTA). The inhibitor, stable on storage at -20 C. was inactivated by heating plasma to 56 C. for 30 minutes. The inhibitor was stable between pH 5 and 9. Inhibitory activity was increased by aluminum hydroxide adsorption and not apparently affected by celite exhaustion of plasma. The inhibitor was present in the fraction of plasma precipitated between 55 and 65 per cent ammonium sulphate saturation and migrated with the alpha globulins electrophoretically. The action of the inhibitor was prevented by soy bean trypsin inhibitor. Inhibitory activity was present in serum and in all normal plasma samples examined as well as in plasma from patients deficient in Hageman factor, PTA factor or factors VIII or IX. The physiologic and pathologic significance of this inhibitor remains to be determined.