1. Methods for the preparation and partial purification of streptococcal fibrinolysin are described.
2. The lysis of fibrin clots in the presence of streptococcal fibrinolysin is associated with proteolysis of the fibrin. Digestion is due to an enzyme normally present in serum or plasma in an inactive state, which is activated by fibrinolysin. Fibrinolysin alone has no demonstrable proteolytic activity.
3. The lysin factor-fibrinolysin system brings about proteolysis of other proteins such as gelatin or casein, in addition to fibrin and fibrinogen.
4. It is suggested that lysin factor exists in serum or plasma as a zymogen, and that it is activated by fibrinolysin, a kinase, in a manner similar to the activation of trypsinogen by enterokinase or the mold kinase of Kunitz (1938).
