ABSTRACT
The powerful surface catalytic action of phospholipids on the activation of plasma coagulation proteins has been recognized for many years. Activation of coagulation factors occurs by limited proteolysis of one or two peptide bonds in the zymogen molecule, a reaction that is catalyzed by another active coagulation factor. Early investigations on phospholipid involvement focused on questions regarding the chemical and physical properties of the phospholipids that were required to exhibit procoagulant activity. Coagulation factors were usually quantitated by relatively complicated clotting assays. The proteins which participate in the different phospholipid-dependent steps of the coagulation cascade not only interact with phospholipids but also bind to each other. The most likely source of procoagulant phospholipid to stimulate tenase and prothrombinase activity in vivo are platelet membrane phospholipids. Phosphatidylserine and phosphatidylinositol are the major negatively charged phospholipids in platelet membranes, amounting to 10 and 4 mol% of the total phospholipid complement, respectively.
