Vitamin K1 2,3-epoxide is a vitamin K derivative. Vitamin K needed for the posttranslational modification of certain proteins, mostly required for blood coagulation. Within the cell, Vitamin K undergoes electron reduction to a reduced form of Vitamin K (called Vitamin K hydroquinone) by the enzyme Vitamin K epoxide reductase (or VKOR). Another enzyme then oxidizes Vitamin K hydroquinone to allow carboxylation of Glutamate to Gamma-cabroxygluatmate (Gla); this enzyme is called the gamma-glutamyl carboxylase or the Vitamin K-dependent carboxylase. The carboxylation reaction will only proceed if the carboxylase enzyme is able to oxidize Vitamin K hydroquinone to vitamin K epoxide at the same time; the carboxylation and epoxidation reactions are said to be coupled reactions. Vitamin K epoxide is then re-converted to Vitamin K by the Vitamin K epoxide reductase. These two enzymes comprise the so-called Vitamin K cycle. One of the reasons why Vitamin K is rarely deficient in a human diet is because Vitamin K is continually recycled in our cells. Vitamin K 2,3-epoxide is the substrate for vitamin K 2,3-epoxide reductase (VKOR) complex. Significantly increased level of serum vitamin K epoxide has been found in patients with familial multiple coagulation factor deficiency. (PMID 12384421) Accumulation of vitamin K1-2,3-epoxide in plasma is also a sensitive marker of coumarin-like activity of drugs. (PMID 2401753) [HMDB]