Activated factor XII, also known as factor XIIa, is a protease enzyme that plays a crucial role in the intrinsic pathway of the coagulation cascade. It is an inactive zymogen that becomes activated upon exposure to negatively charged surfaces, such as subendothelial collagen or platelet phospholipids, during vascular damage or injury.
Factor XII is produced in the liver and circulates in the blood as an inactive precursor. Upon activation, it undergoes a conformational change that enables it to cleave several substances in the coagulation cascade, ultimately leading to the formation of a blood clot.
Activated factor XII initiates the coagulation process by activating factor XI, which subsequently cleaves factor IX to form active factor IXa. This in turn activates factor X, leading to the conversion of prothrombin to thrombin, which is responsible for the conversion of fibrinogen to fibrin. Fibrin forms a network of fibers that trap platelets and red blood cells, resulting in the formation of a stable blood clot.
Beyond its role in coagulation, activated factor XII is involved in other biological processes, such as inflammation and fibrinolysis. It can interact with various plasma proteins, endothelial cells, and platelets, leading to the production of inflammatory mediators or the activation of other proteases involved in the breakdown of blood clots.
Overall, activated factor XII plays a pivotal role in the initiation and amplification of the coagulation cascade, helping to maintain hemostatic balance and prevent excessive bleeding.
