The vitamin K cycle and the anticoagulant effect of VKAs. FII, FVII, FIX, and FX gain full procoagulant activity after conversion of their glutamate residues into γ-carboxyglutamate residues through conversion of reduced vitamin K, to vitamin K epoxide by γ-glutamyl carboxylase. Vitamin K epoxide is recycled by vitamin K epoxide reductase, such that it can be reused. This step is blocked by VKAs because they inhibit vitamin K epoxide reductase.