Vitamin K₂ 2,3-epoxide

Vitamin K2 2,3-epoxide is a vitamin K metabolite occurring in the ubiquinone, secondary metabolite and other terpenoid-quinone biosynthetic pathways. Vitamin K is needed for the post-translational modification of certain proteins, mostly required for blood coagulation. Within the cell, vitamin K undergoes electron reduction to a reduced form of vitamin K by the enzyme vitamin K epoxide reductase. Another enzyme then oxidizes vitamin K hydroquinone to allow carboxylation of glutamate to gamma-carboxyglutamate (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.