The Mode of Action of Vitamin K

An unusual tryptic peptide isolated from the protein, prothrombin, has recently been shown to contain at least a portion of the vitamin K-dependent region of this protein (Nelsestuen, G. L., and Suttie, J. W. (1973) Proc. Nat. Acad. Sci. U. S. A. 70, 3366–3370). A modified glutamylserine dipeptide has been isolated from proteolytic digests of this vitamin K-dependent peptide and has been characterized. It has been unambiguously demonstrated that the glutamic acid of the glutamylserine has been substituted by carboxylation of the γ carbon atom so that the dipeptide structure is: [see PDF for equation] Presumably, the incorporation of the second γ-carboxyl group is dependent on vitamin K.