Activation of Prothrombin With Thrombin

¹ From the Department of Physiology and Pharmacology, Wayne State University College of Medicine, Detroit, Michigan

Mixtures were made consisting of purified prothrombin as substrate (1200 u/ml) and purified thrombin as activator (83 u/ml). The calcium concentration was 0.027 m and the pH 7.2. During an observation time of 90 minutes prothrombin activates and some thrombin is formed. If purified platelet factor 3, or purified platelet cofactor I, or the lipid portion of platelet factor 3, or a certain lipid preparation are also added separately all of the prothrombin substrate becomes thrombin. Each substance is a procoagulant in the sense of functioning in support of thrombin as activator. Each procoagulant is more effective together with Ac-globulin, and even with the latter present sphingosine inhibits the activation of prothrombin by thrombin.