Studies on a Proteolytic Enzyme in Human Plasma

A fraction of globulin was prepared from human plasma which was deficient in prothrombin, thrombin, fibrinogen, plasma thromboplastin, and accelerator globulin. The preparation of globulin contained considerable potential proteolytic activity which could be activated by streptococcal fibrinolysin. This fraction of globulin accelerated the clotting of normal platelet-deficient plasma. However, the clot-accelerating effect of the globulin fraction was the same whether or not its proteolytic property had been activated. The addition of streptococcal fibrinolysin to normal platelet-deficient plasma did not accelerate coagulation. Nor did the addition of streptococcal fibrinolysin to hemophilic platelet-deficient plasma promote its coagulation. The data presented suggest that proteolysis by activated plasma proteolytic enzyme is not an essential stage in the coagulation of the blood.