K for Koagulation Natural: 1) in plants as phylloquinone (or vitamin K1) 2) in intestinal bacterial flora as menaquinone (or vitamin K2) Synthetic: Menadione functions of Vit K The principal role of vitamin K is in the posttranslational modification of various blood clotting factors Carboxylation of certain glutamic acid residues present in these proteins

1. VITAMIN K
Maryam Fida (o-1827)
Source: Lippincott Biochemistry
Illustrated Reviews
World WideWeb

2. Vit. K
■ K for Koagulation
Natural: 1) in plants as phylloquinone (or vitamin K1)
2) in intestinal bacterial flora as menaquinone (or vitamin K2)
Synthetic: Menadione

3. Function of vitamin K
■ The principal role of vitamin K is in the posttranslational modification of
various blood clotting factors
■ Carboxylation of certain glutamic acid residues present in these proteins

4. Clotting Factors

5. Formation of γ-carboxyglutamate
(Gla):
■ Prothrombin (II) and blood clotting factorsVII, IX, and X are synthesized
as inactive precursor molecules
■ Formation of the clotting factors requires the vitamin K–dependent
carboxylation of glutamic acid residues

7. ■ The reaction requires O2, CO2, and vitamin K
■ Reaction inhibited by dicumarol, and by warfarin, a synthetic analog of
vitamin K

8. ■ The Gla residues of prothrombin are good chelators of positively charged
calcium ions, because of the two adjacent, negatively charged
carboxylate groups
■ The prothrombin–calcium complex is then able to bind to phospholipids
essential for blood clotting on the surface of platelets
■ Attachment to the platelet increases the rate at which the proteolytic
conversion of prothrombin to thrombin can occur

10. Distribution and requirement
■ Cabbage, cauliflower, spinach, egg yolk, and liver
■ There is also extensive synthesis of the vitamin by the bacteria in the
gut
■ Adequate Intake (AI) 120µg/day for adult males and 90µg/day for females

11. Absorption
■ Bile salts needed for absorption of K1 and K2
■ Enter blood by way of lymph
■ In plasma are carried in combination with albumin

12. Deficiency ofVitamin K
■ Faulty absorption: lack of bile salts as in obstructive jaundice
■ Diarrhoeal diseases: sprue, celiac disease and ulcerative colitis
■ If the bacterial population in the gut is decreased by antibiotics
■ Administration of drugs having anti-vitamin K activity e.g. warfarin
■ Certain second-generation cephalosporins, for example,
cefoperazone

13. Deficiency of vitamin K in the
newborn
■ Newborns have sterile intestines
■ Lack the bacteria that synthesize vitamin K
■ Human milk provides only about one fifth of the daily requirement for
vitamin K
■ Recommended that all newborns receive a single intramuscular dose of
vitamin K as prophylaxis against hemorrhagic disease

14. Effects of Deficiency
■ Tendency to bleed profusely from minor wounds or even
spontaneously
■ Bleeding from GI tract, urinary tract and uterus; ecchymoses and
epistaxis
■ ProlongedClotting time
■ Increase in Prothrombin time – PT (Prothrombin activity is measured
as prothrombin time)
■ Increase in PT shows a deficiency of prothrombin

15. Toxicity of vitamin K
■ Prolonged administration of large doses of vitamin K can produce
hemolytic anemia and jaundice in the infant, due to toxic effects on the
membrane of red blood cells.