Studies in Blood Coagulation

Crude or crystalline trypsin in proper concentration causes the blood or plasma of human beings, dogs, rabbits, guinea pigs, and horses to coagulate. It does not clot the fibrinogen directly, but reacts with prothrombin to form thrombin. Since trypsin thus has the same effect as the physiological system Ca plus platelets (or Ca plus tissue extracts), it is suggested as a tentative working hypothesis that the latter system contains a proteolytic enzyme with a specific affinity for prothrombin. Other implications of this trypsin effect with respect to the mechanism of physiological coagulation are discussed in the text (pages 557-558). The proteolytic enzyme papain also coagulates blood. In this case the enzyme does not activate prothrombin, but acts directly on fibrinogen to form a fibrillar gel resembling fibrin. If one admits this clot to be fibrin, this constitutes strong evidence that thrombin, the physiological coagulant, is also a proteolytic enzyme with a specific action on fibrinogen.