F 5

Role in the organism:

Coagulation factor V is an essential component of the cascade process of blood coagulation. Blood coagulation is usually initiated by either trauma or injury to the blood vessels and culminates in the conversion of the circulating protein fibrinogen into its derivative fibrin, a protein found in blood clots. Factor V interacts with another coagulation factor, known as factor X, and converts the inactive prothrombin polypeptide into the active enzyme thrombin. Thrombin then converts fibrinogen to fibrin and allows blood clots to form. Factor V and thrombin are in the positive feedback - blood clotting works to intensify this clotting process. This enables rapid blood clotting when the process is needed by the body.

Role in the disorder (state):

Defects in the gene encoding the F V factor block the cascade process of blood coagulation resulting in continuous bleeding, both externally and within the body cavities. However, a special group of mutations (factor V Leiden mutations) have the opposite effect - the carriers of these mutations have a predisposition to more frequent blood clotting, which is manifested by the formation of blood clots. This is because factor V can also inhibit coagulation, (in this case acting as an anticoagulant). Factor V acts like this when it interacts with an anticoagulation protein called activated protein C (APC). If there was no such regulation, blood clotting would be out of control every time we suffered the slightest injury. Leiden mutations at the F V locus prevent the interaction between factor V and APC and therefore affect anticoagulant activity but not its role in the cascade process of blood coagulation.