Vitamin K dependent in vitro production of prothrombin

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Abstract
During [rat] prothrombin biosynthesis, glutamyl residues in prothrombin precursor proteins are carboxylated to .gamma.-carboxyglutamyl residues by a vitamin K dependent carboxylase. Ca-dependent and Ca-independent rat prothrombin antibody subpopulations were produced and utilized to study the liver microsomal precursors of prothrombin that accumulate when vitamin K action is blocked. A substantial portion of the precursor pool accumulating in the vitamin K deficient or warfarin-treated rat will react with a Ca2+-dependent antibody at high Ca concentration and appears to be partially carboxylated. During in vitro incubation in the presence of vitamin K, the fraction of the precursor pool which is tightly bound to the microsomal membrane appears to be the preferred substrate for the vitamin K dependent carboxylation. A small amount of completely carboxylated rather than a large amount of partially carboxylated products are produced during these incubations. Treatment with a Sepharose-bound prothrombin antibody demonstrated that .apprx. 20-25% of the total carboxylated microsomal protein precursor pool consists of prothrombin precursors. This treatment removes an equal amount of total carboxylase activity and the enzyme is active in this carboxylase precursor-antibody complex.