Vitamin-K cycle

Vitamin K plays an important role in blood coagulation and bone formation. Vitamin K obtained from the diet. Once transferred to the cells of the target tissue, vitamin K is metabolized by redox cycling in the intracellular endoplasmic reticulum body, in a process known as the “vitamin-K cycle”. This series of oxidation-reduction reactions begins with conversion of vitamin K from a stable oxidized form (quinone form) to a hydroquinone form by vitamin K epoxide reductase (VKOR). GGCX carboxylates the glutamic acid residues of vitamin K-dependent proteins (coagulation factors F2,F7, F9 and F10, PROS, PROC, and bone factor Osteocalcin (BGLAP) etc…), while simultaneously oxidizing the reduced form of vitamin K to an epoxide form. The epoxide form of vitamin K is reduced by epoxide reductase (VKORC1) to a reduced form and then to the reduced hydroquinone form. This reuse system allows for a very small amount of vitamin K in cells to act efficiently as a cofactor of GGCX in the post-translational carboxylation of VKDPs. Warfarin, an oral anticoagulant drug, inhibits VKOR, stops the vitamin K cycle, and prevents coagulation.