Structural and functional properties of snake venom prothrombin activators.

In this review we have summarized the current knowledge about the prothrombin activating principles present in the venom of a large number of different snake species. It appears that snake venom prothrombin activators can be classified into four different groups based on their structural properties and on their functional properties in prothrombin activation. Group I activators efficiently convert prothrombin into meizothrombin and their activity is not influenced by the non-enzymatic cofactors of the prothrombinase complex (CaCl2, factor Va and phospholipid). Group II and III activators can cleave both peptide bonds in prothrombin necessary to convert prothrombin into thrombin. The prothrombin-converting activity of Group II activators is strongly stimulated by phospholipids and factor Va in the presence of CaCl2, whereas the activity of group III activators is only stimulated by CaCl2 and phospholipid. Group IV consists of snake venom proteases which do not convert prothrombin into enzymatically active products but cleave peptide bonds in prothrombin, resulting in the formation of inactive precursor forms of thrombin.