Carboxylation, the completion step in prothrombin biosynthesis

Abstract It has been found that [ 14 C]CO 2 is incorporated into prothrombin in vivo in two hours. The amount of incorporation is increased 3 to 4 fold by the administration of vitamin K 1 to the warfarin-treated vitamin K-deficient rat, over incorporation in the “normal” rat. The radioactivity is found in one acidic peptide following trypsin digestion and following pronase and aminopeptidase digestion is found in one acidic amino acid. The [ 14 C] is lost on heating of this amino acid at pH 2, leaving unlabeled glutamic acid. It appears that the vitamin K-dependent step in the “completion” of prothrombin is carboxylation of a glutamyl residue of the preformed protein molecule.