Isolation and characterization of vitamin K-dependent region of bovine blood clotting factor X.

A 39-residue peptide from the tryptic digestion of bovine blood clotting factor X has been isolated by specific adsorption on barium citrate. The amino- and carboxyl-terminal sequences of the peptide were determined and compared to the vitamin K-dependent Ca2+-binding region from bovine prothrombin. The factor X peptide was found to contain gamma-carboxyglutamic acid residues, and the results of independent analysis are consistent with all 14 glutamic acid residues as gamma-carboxyglutamic acid. The similarity of the factor X peptide to the prothrombin peptide supports the hypothesis that the vitamin K-dependent blood clotting proteins are descended from a common ancestral gene.