Preparation and properties of prothrombin.

The conversion of prothrombin to thrombin constitutes a major step in blood coagulation. Aside from its important hemostatic function, the reaction has broad biological significance since it is one of the few examples of protein-protein and proteinion interaction with profound physiological as well as pathological effects. As an archetype of such reactions, clearer delineation of the nature of prothrombin, and of the conditions, kinetics, and alterations which occur during thrombin elaboration would be most valuable. Much of this area remains obscure, largely because of difficulties in obtaining adequate materials for study. Despite notable advances in purifying prothrombin, leading to numerous conclusions regarding its composition and activation (l--5), considerable question remains concerning ultimate purity (1, 6). Very recently nonprothrombin entities have been identified and removed from prothrombin fractions formerly considered to be highly purified (7). For some years we have been engaged in purifying human and bovine prothrombin. This paper is intended to report our experiences, and to provide information bearing directly on the question of purity, and the requirements necessary for thrombin formation. Some of the prothrombin preparations were devoid of most, if not all, of the other known coagulation factors. Other fractions were prepared intentionally contaminated with Factor VII and probably other clotting constituents.