Central regulator of hemostasis. It serves as a critical cofactor for the prothrombinase activity of factor Xa that results in the activation of prothrombin to thrombin. Inhibited by SERPINA5. Factor Va, the activated form of factor V, is composed of a heavy chain and a light chain, non-covalently bound. The interaction between the two chains is calcium-dependent. Forms heterodimer with SERPINA5. Plasma. Domain B contains 35 x 9 AA tandem repeats, and 2 x 17 AA repeats. Thrombin activates factor V proteolytically to the active cofactor, factor Va (formation of a heavy chain at the N-terminus and a light chain at the C-terminus). Sulfation is required for efficient thrombin cleavage and activation and for full procoagulant activity. Activated protein C inactivates factor V and factor Va by proteolytic degradation. Phosphorylated by FAM20C in the extracellular medium. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Disease susceptibility is associated with variants affecting the gene represented in this entry. Disease susceptibility is associated with variants affecting the gene represented in this entry. Disease susceptibility is associated with variants affecting the gene represented in this entry. Belongs to the multicopper oxidase family. Factor V entry