Protein which possesses at least one gamma-carboxyglutamic acid, a vitamin K dependent post-translational modification of a glutamate residue found in blood coagulation proteins and in the proteins of calcified tissues. Gamma-carboxyglutamyl residues are good chelators of calcium ions. There are two natural forms of vitamin K, which are phylloquinone (vitamin K1 or phytylmenaquinone) in green vegetables and menaquinone (vitamin K2 or menaquinone-n, depending of the number of isoprene units of the side-chain or MK-n) in intestinal bacteria, as well as one synthetic provitamin form, menadione (vitamin K3). In infants, the primary symptom of a deficiency of this fat-soluble vitamin is a hemorrhagic syndrome.