Vitamin k (Lippincott Biochemistry Illustrated Reviews World Wide Web)

Vitamin k (Lippincott Biochemistry Illustrated Reviews World Wide Web)

• 1.
  VITAMIN K Maryam Fida(o-1827) Source: Lippincott Biochemistry Illustrated Reviews World WideWeb
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  Vit. K ■ Kfor Koagulation Natural: 1) in plants as phylloquinone (or vitamin K1) 2) in intestinal bacterial flora as menaquinone (or vitamin K2) Synthetic: Menadione
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  Function of vitaminK ■ 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
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  Clotting Factors
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  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
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  ■ The reactionrequires O2, CO2, and vitamin K ■ Reaction inhibited by dicumarol, and by warfarin, a synthetic analog of vitamin K
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  ■ The Glaresidues 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
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  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
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  Absorption ■ Bile saltsneeded for absorption of K1 and K2 ■ Enter blood by way of lymph ■ In plasma are carried in combination with albumin
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  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
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  Deficiency of vitaminK 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
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  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
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  Toxicity of vitaminK ■ 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.