ABSTRACT
Although the list of biochemical and biological actions attributed to thrombin continues to grow, the term thrombinlike as applied to venom enzymes generally implies only the capacity to induce the clotting of fibrinogen. Evidence for the existence of thrombinlike venom enzymes dates back several decades, and recent studies have established their identity in molecular detail. Most of the thrombinlike enzymes now identified have been in the pit viper family, but some enzymes have also been found in the venoms of the true vipers, Bitis gabonica and Cerastes vipera, and a colubrid, Dispholidus typus. The thrombinlike venom enzymes are serine proteinases, inactivated by diisopropylphosphofluoridate or phenylmethanesulfonyl fluoride and, less regularly, by chloromethyl ketones of lysine and arginine derivatives. The induction of defibrinogenation by thrombinlike venom enzymes appears to be mediated mainly by plasmic digestion of fibrin, and possibly fibrinogen, triggered indirectly by actions of the venom enzymes.
