Purification of M5, a fibrinolytic proteinase from Crotalus molossus molossus venom that attacks complement.

Crotalus molossus molossus (northern blacktailed rattlesnake) venom contains agents that affect blood coagulation. A fibrin(ogen)olytic proteinase, called M5, was isolated and purified from this venom by ion exchange chromatography in a two-step procedure. M5 consists of a single non-glycosylated polypeptide chain with a molecular weight of 25 kDa and an isoelectric point of 7.6. It hydrolyses the A alpha and B beta chains of fibrinogen and the alpha and beta chains of fibrin. It also exhibits caseinolytic activity, but has no effect on synthetic substrates cleaved by thrombin, plasmin, kallikrein, or trypsin. The proteolytic activity of the enzyme against fibrinogen, fibrin, and casein is inhibited by ethylenediaminetetraacetic acid (EDTA) and the loss of activity by EDTA treatment can be prevented by addition of Zn2+. This suggests that M5 is a zinc metalloproteinase. M5, at doses of 50 micrograms and higher, induces significant hemorrhage when injected subcutaneously into mice. In addition, it inactivates guinea-pig complement in a dose-dependent fashion and hydrolyses human C2, C3, and C4.