Vitamin K

 
Vitamin K (phylloquinone) is a lipid vitamin found in plants as K₁, or phytylmenaquinone, and in bacteria as K₂, or multiprenylmenaquinone. Vitamin K is related to ubiquinone [Monday's Molecule #10]. Ubiquinone serves as an electron carrier in reactions such as membrane-associated electron transport [Ubiquinone and the Proton Pump]. Related cofactors in plants (plastoquinone) and bacteria (menaquinone) can be absorbed in the intestine and converted to vitamin K.


Although we can't synthesize vitamin K ourselves, we usually get enough of it from intestinal bacteria. Vitamin K deficiency is not common for this reason. The most common symptom of vitamin K deficiency is hemorraging due to a defect in blood clotting. The symptoms are frequently seen in newborn babies, especially those born prematurely because they lack intestinal bacteria. This is why premature babies are given vitamin K.

Vitamin K is a cofactor in reactions required for the synthesis of some of the proteins involved in blood coagulation. It is the coenzyme for a mammalian carboxylase that catalyzes the conversion of specific glutamate residues to γ-carboxyglutamate residues. The reduced (hydroquinone) form of vitamin K participates in the carboxylation as a reducing agent.