Vitamin K Vitamin K is a group of

Vitamin K • Vitamin K is a group of lipophilic, hydrophobic vitamins. • They are needed for the postranslation modification of proteins required for blood coagulation, • They are involved in metabolism pathways, in bone mineralisation, cell growth, metabolism of blood vessel wall.

Vitamin K 1 • Vitamin K 1 (phylloquinon) – plant origin • Vitamin K 2 (menaquinon) – normally produced by bacteria in the large intestine • K 1 a K 2 are used differently in the body Vitamin K 2 – K 1 – used mainly for blood clothing – K 2 – important in non-coagulation actions - as in metabolism and bone mineralization, in cell growth, metabolism of blood vessel walls cells. Synthetic derivatives of Vit. K

Vitamin K - function • Cofactor of liver microsomal carboxylase which carboxylates glutamate residues to g-carboxyglutamate during synthesis of prothrombin and coagulation factors VII, IX a X (posttranslation reaction). • Carboxylated glutamate chelates Ca 2+ ions, permitting the binding of blood clotting proteins to membranes. • Forms the binding site for Ca 2+ also in other proteins – osteocalcin.

Physiological Effects of Vitamin K • Vitamin K serves as an essential cofactor for a carboxylase that catalyzes carboxylation of glutamic acid residues on vitamin Kdependent proteins. These proteins are involved in: 1) Coagulation 2) Bone Mineralization 3) Cell growth

Vitamin K Deficiency Deficiencies are very rare in humans except in newborns due to: • insufficient gut bacteria • poor placental transport of vitamin K • low prothrombin synthetic capacity of neonatal liver Newborns routinely receive vitamin K injection (0. 5 -1 mg vitamin K) or 2 mg orally, because human milk is very low in vitamin K (2. 5 μg/L). Bleeding episodes may occur in patients with low vitamin K status on long-term antibiotic treatment (loss of colonic bacteria).

Vitamin K Deficiency GI Bleeding Hemorrhagic disease of the newborn

Vitamin K - deficiency • Deficiency is caused by fat malabsorption or by the liver failure. • Blood clotting disorders – dangerous in newborns, life -threatening bleeding (hemorrhagic disease of the newborn). • Osteoporosis due to failed carboxylation of osteokalcin and decreased activity of osteoblasts. • Under normal circumstances there is not a shortage, vit. K is abundant in the diet.

Sources of vitamin K • • Green leafy vegetables vegetable oil broccoli cereals http: //health. allrefer. com/health/nutrition. html

Coagulation • The transformation of liquid blood into a solid gel • Stops blood flow in the damaged area • Fibrin is the final protein which produces a meshwork to trap RBC and other cells

Vitamin K Dependent Coagulation • Certain clotting factors/proteins require calcium to bind for activation • Calcium can only bind after gamma carboxylation of specific glutamic acid residues in these proteins • The reduced form of vitamin K 2 (vitamin KH 2) acts as a cofactor for this carboxylation reaction. • These proteins are known as “Vitamin K dependent” proteins

Vitamin K Dependent Proteins • • • factor II (prothrombin) factor VII (proconvertin) factor IX (thromboplastin component) factor X (Stuart factor) protein C & protein S Protein Z

Clotting Cascade