The occurrence of beta-hydroxyaspartic acid in the vitamin K-dependent blood coagulation zymogens

Previous work has shown that two vitamin K-dependent plasma zymogens, factor X and protein C, each contain one residue of erythro-beta-hydroxyaspartic acid. In the present study, prothrombin, factor VII and factor IX were subjected to amino acid analyses for beta-hydroxyaspartic acid. Factor IX and factor VII each contain one residue of erythro-beta-hydroxyaspartic acid. Edman sequence analyses revealed that this residue occurs at position 64 in human and bovine factor IX. Inasmuch as the nucleotide sequence codes for aspartic acid at this position, it appears highly likely that beta-hydroxyaspartic acid is formed in these proteins by a post-translational hydroxylation of aspartic acid. In contrast, neither human nor bovine prothrombin contain beta-hydroxyaspartic acid.