Vitamin K and the Clotting of Blood

Department or Chemistry, Visva-Bharati, Santiniketan-731 235, India V1tamin K mediates the formation of active prothrombin inside the liver, from the physiologically inactive precursor protein through the post ribosomal modification occurring after the completion of the synthesis of the polypeptide chain or the precursor. The activity or vitamin K centers round the formation of ten additional carboxyl groups attached to one each of the gamma (\(\gamma\))-carbon atom of the ten glutamic acid residues situated towards the N-terminal region of the prothrombin molecule at positions 7, 8, 15, 17,10, 21, 26, 27, 30 and 33. This carboxylated fragment I of the normal prothrombin molecule having the ten \(\gamma\)-carboxyglutamic acid residues in the chain of 42 amino acids at positions 1 to 42, is responsible for binding calcium ions and subsequent complexing with phospholipids and advancing proper conformation so that the prothrombin molecule may interact suitably with the physiological activators and is cleaved at the peptide bonds located between arginine and threonine at positions 274-275, as well as the bond between arginine and isoleucine at positions 323-324 to be activated to thrombin which subsequently converts the circulating fibrinogen to fibrin. The reactivity of vitamin K is exerted through its formation of a reduced intermediate