Hementerin is a metalloprotease found in the saliva of a hematophagous leech, Haementeria depressa, which is responsible for the anticoagulant property of the animal's bite to prolong blood sucking from the host.
Hementerin is a protease, i.e., it carries out an enzymatic cleaving of a plasma protein involved in rapid blood coagulation called fibrinogen.
The absence of a significant amount of plasma fibrinogen retards coagulation, thus it is a naturally occurring anticoagulant.
Hementerin breaks the alpha (FGA), gamma (FGG) and beta (FGB) chains, by degrading cross-linked fibrin.
In addition, hementerin inhibits platelet aggregation induced by collagen via the activation of a nitridergic pathway.