Summary
Two proteins presenting anticoagulant activities were isolated from Viperidae venoms : one from Vipera aspis, the other from Vipera berus. They interfere with the formation of prothrombinase. Their inhibitory effect results from a specific action of a complex which blocks the active sites of phospholipids. This complex is easily dissociated by antivenoms allowing normal clot formation.
Berus inhibitor possesses a high phospholipase activity while aspis inhibitor is completely devoid of this activity. The anticoagulant action of these venom factors does not appear to be enzymatic.
The affinity of both inhibitors for phospholipids seems similar though aspis inhibitor shows a more marked anticoagulant action which is neutralized by the addition of a greater amount of phospholipid.
The study of these venom inhibitors confirms the fact that, in the absence of platelet phospholipids, clot formation is not possible.
