What Happens to Vitamin [K.Sub.1] in Serum After Bone Fracture?(Technical Briefs‪)‬

We wished to investigate the mechanism of decreased serum vitamin [K.sub.1] after bone fractures. Vitamin [K.sub.1] plays a role in bone formation because it is required as a cofactor for the transformation of glutamic acid (Glu) residues on proteins to [gamma]-carboxyglutamic acid (Gla) residues. The double carboxy group on Gla residues has high affinity for the binding of calcium. Bone formation involves vitamin K-dependent small peptide osteocalcin (boneGla-protein) that is secreted by osteoblasts. Serum concentrations of vitamin [K.sub.1] reflect in part the capacity of the serum to carry the vitamin. Vitamin [K.sub.1] is a lipid, and little is known about the binding of this vitamin to proteins other than that it is transported in serum by the lipoproteins. It is not known whether there is a specific "vitamin [K.sub.1]-binding protein' in tissues as has been suggested for vitamin E as a "tocopherol-binding protein' (1).