Prothrombin

Prothrombin is an inactive form of coagulation factor II. It is produced by the liver and its formation is dependent on the presence of vitamin K. Using a complex of substances known as prothrombin activator, prothrombin is activated to thrombin.

Source
ŠVÍGLEROVÁ, Jitka. Protrombin [online]. Poslední revize 18. 2. 2009, [cit. 12.11.2010]. < https://web.archive.org/web/20130512184556/http://wiki.lfp-studium.cz/index.php/Protrombin >