ABSTRACT
Vitamin K, a fat-soluble vitamin, is an enzyme cofactor for posttranslational modi‚cation of a select group of proteins. In the presence of vitamin K, speci‚c glutamate residues are converted into γ-carboxyglutamic acid (Gla) residues by a vitamin K-dependent (VKD) carboxylase. The VKD coagulation proteins, factors II, VII, IX, and X, and proteins C, S, and Z, are synthesized in the liver (Berkner, 2005). The extra-hepatic VKD proteins include osteocalcin (Hauschka et al., 1975; Price et al., 1976), Matrix Gla-protein (Price et al., 1983), Gla-rich protein (Viegas et al., 2008), periosin (Coutu et al., 2008), Tgfbi (Ahmed et al., 2007; Zhang et al., 2009), and Gas-6 (Shearer, 2000; Berkner and Runge, 2004).
