Vitamin k

Chemistry of Vitamin K, Biochemical role of Vitamin K, Recommended dietary allowance of Vitamin K, Dietary sources of Vitamin K, Deficiency symptoms of vitamin K, Hypervitaminosis of vitamin K, Toxicity of Vitamin K

1. Jasmine Juliet .R Biotechnology Department Agricultural college and Research & Institute Madurai . Chemistry, Biochemical Role, RDA, Deficiency diseases of Vitamin K

2. Vitamin K - Introduction Vitamin K is the only fat soluble vitamin with a specific Coenzyme function. It is required for the production of blood clotting factors, essential for coagulation ( in German - Koagulation ; hence the name K for this vitamin).

3. Vitamin K - Chemistry Vitamin K exists in different forms . Vitamin K1 ( Phylloquinone ) is present in plants . Vitamin K2 ( menaquinone ) is produced by the intestinal bacteria and also found in animals. Vitamin K3 ( menadione ) is the synthetic form .

4. Vitamin K - Chemistry All the three vitamins (K1, K2, K3) are napthoquinone derivatives . Isoprenoid side chain is present in Vitamin K1, and K2. All the three are stable to heat. Their activity is, however , lost by oxidizing agents, irradiation, strong acids and alkalies .

5. Vitamin K – biochemical Functions I. The function of vitamin K are concerned with blood clotting process. It brings about the Translational (after protein synthesis in the cell) modification of certain blood clotting factors . The clotting factors II ( Prothrombin ) ,VII, IX, and X are synthesised as inactive precursors (zymogens) in the liver .

6. Vitamin K – biochemical Functions II. Vitamin K acts as a coenzyme for the carboxylation of glutamic acid ( to form γ- carboxy glutamate) residues present in the proteins and the reaction is catalysed by a carboxylase ( microsomal ).

7. Vitamin K - RDA Strictly speaking, there is no RDA for vitamin K, since it can be adequately synthesised in the gut. It is however, recommended that half of the body requirement is provided in the diet, while the other half is met from the bacterial synthesis. Accordingly , RDA for an adult is 70-140 μg /day.

8. Vitamin K - Dietary sources Cabbage , Cauliflower, tomatoes, alfa alfa , spinach and other green vegetables are good sources. It is also present in egg yolk, meat, liver, cheese and Dairy products.

9. Vitamin K - Deficiency symptoms The deficiency of vitamin K is uncommon , since it is present in the diet in sufficient quantity and/or is adequately synthesised by the intestinal bacteria. Deficiency of vitamin K leads to the lack of active prothrombin in the circulation. The result is that blood coagulation is adversely affected . The individual bleeds profusely even for minor injuries. The blood clotting time is increased .

10. Vitamin K - Hypervitaminosis Administration of large doses of vitamin K produces hemolytic anaemia and jaundice, particularly in infants. The toxic effect is due to increased breakdown of RBC.

11. Antagonists of Vitamin K The compound - namely heparin , bishydroxy coumarin - act as anticoagulants and are antagonists to vitamin K. The salicylates and dicumarol are also antagonists to vitamin K. Dicumarol is structurally related to vitamin K and acts as a competitive inhibitor in the synthesis of active prothrombin .