Function of Ac-Globulin Utilizing TAMe Synthetic Substrate Assay Method For Determination of Prothrombin

¹ From the Departments of Medicine and Obstetrics, the University of Cincinnati College of Medicine, and the Cincinnati General Hospital, Cincinnati, Ohio

Studies employing a synthetic substrate tosyl arginine methyl ester (TAMe) for the measurement of plasma prothrombin have been utilized to study the function of Ac-globulin. In aged plasmas grossly deficient in this factor, most of the prothrombin initially present in the plasma before storage can be recovered, provided that the thrombin evolving slowly from prothrombin is protected from destruction by antithrombin. The presence of dilute TAMe in the activation mixture appears to perform this function. In stored plasma deficient in Ac-globulin, the efficiency of a specific quantity of accelerator can be increased 10-fold, provided that dilute TAMe, serving to inhibit antithrombin, is present in the activation mixture. Species differences in accelerators, observed with clotting studies, can be largely eliminated, provided that dilute TAMe is present while thrombin is evolving from prothrombin. Experiments with purified prothrombin, free of accelerators and inhibitors, confirm the observations obtained with Ac-globulin-deficient plasma. The activation of purified prothrombin is inhibited by serum. Dilute TAMe effectively blocks this inhibiting effect, allowing for normal activation of the prothrombin. The evidence presented indicates that Ac-globulin acts as a true accelerator, which does not enter into stoichiometric combination with prothrombin.

Note:
with the technical assistance of Roberta Eckert