Gamma Carboxylation of what requires vitamin K

Biochemical functions of Vitamin K The functions of vitamin K are concerned with blood clotting process. lt brings about the post- translational (after protein biosynthesis in the cell) modification of ceain blood clotting factors. The clotting factors ll (prothrombin), Vil, lX and X are synthesized as inactive precursors (zymogens) in the liver. Vitamin K acts as a coenzyme for the carboxylation of glutamic acid residues present in the proteins and this reaction is catalysed by a carboxylase (microsomal). lt involves the conversion of glutamate (Clu) to y-carboxyglutamate (Gla) and requires vitamin K, O2 and COz. The formation of y-carboxyglutamate is inhibited by dicumarol, an anticoagulant found in spoilt sweet clover. Warfarin is a synthetic analogue that can inhibit vitamin K action Vitamin K is also required for the carboxylation of glutamic acid residues of osteocalcin, a calcium binding protein present in the bone. The mechanism of carboxylation is not fully understood. lt is known that a 2,3-epoxide derivative of vitamin K is formed as. an intermediate during the course of the reaction. Dicumarol inhibits the enzyme (reductase) that conves epoxide to active vitamin K. Ref : Biochemistry by U. Satyanarayana 3rd edition Pgno : 130