Factor x

Enzyme that is synthesized in the liver and is vitamin K dependent. In its activated form it forms the complex prothrombinase with Ca++ and phospholipids, which activates prothrombin to form thrombin. When F-X is activated, the extrinsic and intrinsic systems meet.
The molecular weight of F-X is 59,000 D. The half-life is 24-60 hours, the plasma concentration is 1.2 mg/dl.

In 1947, Owren proved that in addition to the already known proacelin, another factor is needed to convert prothrombin into thrombin.
In 1956 and 1957 Hougie and Telfer were able to solve this problem. They found a clotting defect in a lay preacher named Stuart and a young woman named Power in the form of an overlong prothrombin period, which could be normalised by adding serum from healthy people. In another experiment, they were able to show that the prothrombin is also compensated by the addition of factor VII-deficient plasma.
In addition - unlike in the case of factor VII deficiency - this coagulation defect could be compensated in vitro by the addition of the toxin of the Russel viper. Consequently, it was deduced that a factor different from the factors previously known must be present. Because this factor was discovered in Mr. Stuart and Mrs. Power, the factor was named in their honour.

The group of anticoagulants whose point of action is the activated factor X plays a major therapeutic role: these are:

Raviroxaban (Xarelto®)

Apixaban (Eliquis®)

Edoxaban (Lixiana®)

1. HA Neumann (2014) The coagulation system. ABW Scientific Publisher GmbH Berlin S.63f