Retractoenzyme - see platelet factor 6.
Platelet factor 6, also known as retractoenzyme, is an enzyme that is involved in blood clotting. It is released from platelets (blood platelets) during blood clotting and activates factor XI, starting the coagulation cascade. Retractoenzyme plays an important role in the formation of a blood clot and stopping bleeding. A deficiency of this enzyme can lead to blood clotting disorders.