Prothrombin

Prothrombin (factor II) is an enzyme synthesized in the liver and is vitamin K-dependent.

The biosynthesis of prothrombin takes place from a single peptide chain. The prothrombin has a molecular weight of 69,000 D. In electrophoresis it is detectable in the alpha-2 or beta fraction. It carries 10 Ca++ binding sites per molecule to which the prothrombinase binds. The plasma concentration is 10-15 mg/dI. Prothrombin is also detectable in the lymph and extravasally.

The half-life of factor II is 41-72 hours. Prothrombin is activated by the prothrombinase complex(F-Xa, phospholipids, Ca++, factor Va) to form thrombin (factor IIa).
The prothrombin fragments are a measure of thrombin formation and thus also of the activity of the coagulation system.

The prothrombin concentration is given in percent (normally approx. 100%). Prothrombin is increased after administration of vitamin K, under ovulation inhibitors, in the context of hyperlipidemia and in the early phase of consumption coagulopathy.

1. HA Neumann (2014) The coagulation system. ABW-Wissenschaftsverlag GmbH Berlin S. 50f.