Isolation of a fibrinolytic protease, M4, from venom of Crotalus molossus molossus (northern blacktail rattlesnake).

M4, a fibrinolytic protease, was isolated from the venom of Crotalus molossus molossus. It has a pI of 9.6 and a molecular weight of 27,000. The protease hydrolyzes the A alpha and B beta chains of fibrinogen, and the alpha and beta chains of fibrin. This activity was inhibited by EDTA and restored by Ca2+ or Zn2+, but not Mg2+. The protease hydrolyzed hide power azure and casein, but it had no effect on collagen, hyaluronic acid, complement or synthetic substrates for thrombin, plasmin or kallikrein. Subcutaneous injections into mice with doses as high as 100 micrograms did not cause hemorrhage. This protease may have therapeutic use as a thrombolytic agent.