Factor v

The factor V is an alpha-2-globulin with a molecular weight of 330,000 D. It is produced in the liver, endothelium and megakaryocytes. Its half-life is 12-15 hours. In a complex together with factor Xa, Ca++ and phospholipids (prothrombinase) it acts as a cofactor in the catalysis of prothrombin into thrombin. The plasma concentration is 4-14 mg/l or 60-120%.
The factor V is a non-enzymatic cofactor. It is activated by cleavage of peptides by the thrombin. Furthermore, F-V is activated by F-Xa, papain and the venom of the Russel viper. In cases of severe liver damage, the F-V concentration is lowered. Detection is done immunologically by F-V antigen or by so-called one-step tests.

Paul Owren was born in Faaberg, Norway in 1905 and studied medicine in Oslo. After eight years as a general practitioner, he began a career as an internist at the Rikshospitalet in Olslo, becoming Professor of Internal Medicine in 1949. His work included research into factors V and VII, their regulation and the processes of platelet adhesion.

Armand Quick and Paul A. Owren independently discovered factor V. Quick was able to observe that blood that had been rendered uncoagulable by citrate (Ca++ binder) became coagulable again by adding plasma. He recognized that this factor was independent of prothrombin and initially called it "labile factor". Independently of Quick, Owren examined the blood of a patient with an extreme bleeding tendency. He observed an abnormal prothrombin time, which was normalised by adding plasma from which the prothrombin had been removed. This factor was called proakzelerin, later factor V.

1. HA Neumann (2014) The coagulation system. ABW-Wissenschaftsverlag GmbH Berlin S. 56f.