Studies in Blood Coagulation V, the Coaoulation of Blood by Proteolytic ~nzymes

In 1916, Douglas and Colebrook noted that blood coagulation was accelerated by the addition of trypsin. A year later, Heard reported that trypsin could actually coagulate oxalated blood, and ascribed the phenomenon to a hypothetical disturbance in the Ca and P content of the fibrinogen, induced by the enzyme. These two reports were apparently overlooked by workers in the field. In 1928, Waldschmidt-Leitz and his coworkers also reported that trypsin accelerated blood coagulation. They considered their experiments to prove that thrombin was a proteolytic enzyme either identical with or closely related to trypsin; that coagulation was due to the enzymic hydrolysis of fibrinogen to an insoluble modification; and that trypsin accelerated coagulation insofar as it hastened this hydrolysis. They found other proteolytic enzymes, including papain, to be inactive. Mellanby (1935 b) re-investigated the action of trypsin on blood plasma and concluded that the coagulation observed by Heard was due simply to traces of calcium in the commercial preparations of trypsin, and was wholly unrelated to the enzyme as such. The present observations grew out of a chance re-discovery of Heard's observation: certain mixtures of citrated horse plasma and trypsin were found to have clotted when examined after several hours. The participation of calcium could be excluded. Human, guinea pig, dog, horse, and rabbit plasma or blood could be similarly coagulated, provided only that one used the correct concentration of trypsin. Since the phenomenon promised to throw considerable light on the mechanism of physiological coagulation, it was studied in some detail. 543