Factor V

  • OMIM: 227400
  • UniProt: P12259
  • MGI: 88382

Proaccelerin (also Proakzelerin or factor V ) is a protein involved in blood clotting. In contrast to the other involved clotting factors, it has no enzymatic function, but only serves as a cofactor. The protein has a molecular mass of 251 671 daltons and belongs to the group of α - globulins. Its plasma concentration is approximately 10 mg / l, the synthesis takes place probably in the liver.


The gene for Proaccelerin is located on the first chromosome ( 1q23 ).


Proaccelerin circulates in plasma, and has a half-life of about 12 hours. It is activated by thrombin in which it in two chains, a "heavy " ( molecular mass 110 kDa) and one "light " ( molecular mass 73 kDa) is cleaved, which are not covalently bonded to each other by calcium.

The activated form of Proaccelerin also Accelerin or factor Va ( factor previously VI) known as a cofactor of the Stuart - Prower factor ( factor X), prothrombin ( Factor II) is converted to thrombin.

Proaccelerin is degraded by the activated protein C by proteolysis and thus rendered ineffective. This is one of the most important natural inhibition mechanisms of blood coagulation.


There are several genetic disorders which are based on a malfunction of the Proaccelerin. A Proaccelerinmangel caused a rare mild form of hemophilia, the so-called para hemophilia or Owren 's syndrome. This occurs with an incidence of 1:1,000,000 and is inherited as an autosomal recessive trait.

Other mutations of the Proaccelerins cause venous thrombosis. They are the most common cause of inherited thrombophilia (increased blood clot formation). In the most common, the factor V Leiden mutation, the amino acid arginine at position 506 replaced by glutamine ( R506Q ). All Proaccelerin prothrombotic mutations ( factor V Leiden mutation, factor V Cambridge mutation, factor V Hong Kong mutation) cause a resistance of Accelerins to cleavage by activated protein C (so-called APC resistance ). Therefore, it remains active and increases the formation of thrombi.

History of Research

Proaccelerin was discovered in 1947 by Paul Owren ( 1905-1990 ). The complete amino acid sequence was founded in 1987 by Jenny et al. published.