A Normal Inhibitor of the Blood Coagulation Contact Reaction Product

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

Submitted on April 30, 1964 Accepted on July 14, 1964