The mode of action of vitamin K. Isolation of a peptide containing the vitamin K-dependent portion of prothrombin.

Previous evidence has indicated that vitamin K functions in a metabolic step that specifically alters a precursor protein and converts it to biologically active prothrombin. This alteration appears to be related to the biosynthesis or attachment of a noncarbohydrate prosthetic group [Nelsestuen and Suttie (1972) J. Biol. Chem. 247, 8176]. We report the isolation of a peptide from bovine prothrombin that contains the vitamin K-dependent region of the molecule. The properties of the isolated peptide would appear to account for the major differences observed between prothrombin and its biologically inactive form produced by animals administered Dicumarol orally. These differences are quantitative absorption onto insoluble barium salts and the ability to bind calcium ions. The observed properties of this peptide provide direct evidence for the presence of a covalently bound noncarbohydrate prosthetic group(s) on the prothrombin molecule.