Proteolytic Activity of Dog Blood *

Although there is little doubt that more than one proteolytic enzyme occurs in plasma, plasmin (fibrinolysin) is the only such enzyme which has been definitely identified. Astrup and Permin,12 on the basis of differences in susceptibility to activation by streptokinase and fibrinokinase, have suggested that there are two precursors of fibrinolytic enzymes in human blood. They have designated the enzymes activated by streptokinase and fibrinokinase, respectively, as s-plasminogen and f-plasminogen, the latter being responsible for the spontaneous proteolytic activity of blood. The suggestion of Astrup and Permin that the enzyme producing the spontaneous proteolytic activity of serum is not identical with plasmin, which requires external activators such as chloroform or bacterial kinases, was investigated in the dog, and the results are reported in this paper.