Partially carboxylated prothrombins: III. Carboxylation studies

Abstract

Vitamin K-dependent carboxylation of partially carboxylated prothrombins, containing 7-, 5-, 2-, 1- and 0γ-carboxyglutamic acid residues, was studied with Sepharose-bound carboxylase isolated from the microsomal fraction of warfarin-treated bovine liver. The 14CO 2 incorporation was slowest for the 7-carboxyglutamyl variant, intermediate for the 5- and fastest for the 2-, 1- and 0-carboxyglutamyl proteins, these latter three being similar to each other. The carboxylation kinetics for the protein substrate(s) were complex because of the presence of multiple sites. The apparent K m of the 7-carboxyglutamyl variant was, however, the lowest. The CO 2 incorporation requiring vitamin K occurred in the specific glutamic acid residues, as the 10-carboxyglutamyl (normal) prothrombin did not undergo carboxylation.