A variant of prothrombin induced in cattle by prolonged administration of warfarin.

Cows on long term Warfarin therapy produce a form of prothrombin which, although it binds to barium citrate, has a low biological activity. Activation experiments on this form of prothrombin show that it is only slowly converted to thrombin in the presence of Ca2+, although the thrombin produced has normal activity. Further experiments show that the Fragment 1 region of the molecule has a reduced calcium binding capacity. The results indicate the existance of a partially carboxylated form of prothrombin.