The Influence of Contact and Prothrombin on Intermediate Product I Formation

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Abstract
In the in vitro generation of intermediate product I, in which non-purified components are used, both prothrombin and foreign surface “contact” are essential for the formation of optimum activity. Most of the time interval required before optimum intermediate product I activity is reached is the time needed for potentiation of intermediate product I as well as for the conversion of prothrombin to thrombin. In the system studied, it is felt that, in the absence of prothrombin, intermediate product I activity is blocked by the presence of an inhibitor. The action of thrombin would then be to overcome the inhibitor. The apparent increase in factor IX activity, observed during the generation of intermediate product I as measured by the one-stage method, is due to the non-specific clot-promoting effect of intermediate product I on the assay. * Investigation carried out during the tenure of a Special Fellowship from the American Heart Institute, United States Public Health Service.