Vitamin K and the Biosynthesis of Prothrombin V. -pCARBOXYGLUTAMIC ACIDS, THE VITAMIN K-DEPENDENT STRUCTURES IN PROTHROMBIN*

Tryptic peptides obtained from normal prothrombin have been compared with those obtained from prothrombin synthesized by cattle given the vitamin K antagonist dicumarol. Two peptides were found which contain vitamin K-dependent structures. These peptides contain residues 4 through 10 and residues 12 through 44, respectively. One of these (residues 4 through 10) has previously been shown to contain y-carboxyglutamic acid residues. Digestion of this peptide with aminopeptidase M and carboxypeptidase B yielded a tetrapeptide (residues 6 through 9). Mass spectra of this peptide showed that it has the structure Leu-Glu(CO,)-Glu(CO,)-Val. The structure of the peptide containing residues 12 through 44 was determined by automated degradation in a peptide sequenator. The modified glutamic acid residues were identified by mass spectrometric comparison with the thiohydantoin derivatives of synthetic y-carboxyglutamic acid. This approach unequivocally demonstrated that all of the first 10 glutamic acid residues in prothrombin are carboxylated to form y-carboxyglutamic acid residues. Evidence is also presented that indicates that these y-carboxyglutamic acid residues constitute the entire vitamin K-dependent modification of prothrombin