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Biochemistry of Vitamin K GIT | 1 Lecture | Dr. Usman Ghani.

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Presentation on theme: "Biochemistry of Vitamin K GIT | 1 Lecture | Dr. Usman Ghani."— Presentation transcript:

1 Biochemistry of Vitamin K GIT | 1 Lecture | Dr. Usman Ghani

2 Overview Types and chemistry of vitamin K Sources and daily requirements Functions: Synthesis of  -carboxyglutamate in:  Prothrombin and blood clotting factors  Osteocalcin  Interaction of prothrombin with platelets Deficiency and disorders Clinical manifestations

3 Types and Chemistry Occurs in several forms: Vitamin K 1 (Phylloquinone) Vitamin K 2 (Menaquinone) Vitamin K 3 (Menadione) – synthetic form

4 Types and Chemistry Vitamin K 1 (Phylloquinone) Vitamin K 2 (Menaquinone) Vitamin K 3 (Menadione)

5 Sources of Vitamin K Phylloquinone: Green leafy vegetables Menaquinone: Intestinal bacteria  Intestinal bacterial synthesis meets the daily requirement of vitamin K even without dietary supplement Menadione: synthetic form

6 RDA for Vitamin K (  g/day) Infant (0-1 year): 2-2.5 Children (1-8): 30-55 Men (19+): 120 Women (19+): 90 Pregnancy / lactation: 90 / 90 UL: Not established

7 Functions of Vitamin K Coenzyme for the synthesis of prothrombin and blood clotting factors in the liver  Prothrombin and clotting factors are protein in nature  Synthesis of prothrombin, clotting factors VII, IX, X require carboxylation of their glutamic acid (Glu) residue

8 Active form Warfarin

9 Functions of Vitamin K  Mature prothrombin and clotting factors contain  -carboxyglutamate (Gla) after carboxylation reaction  Vitamin K is essential for the carboxylase enzyme involved  Dihydroquinone form of vitamin K is essential for this reaction

10 Active form Warfarin

11 Functions of Vitamin K Anticoagulant drugs: warfarin and dicoumarol  Structural analogs of vitamin K They inhibit the activation of vitamin K to hydorquinone form Hence prothrombin and clotting factors are not carboxylated Blood coagulation time increases upon injury

12 Prothrombin – platelet interaction

13 Functions of Vitamin K Prothrombin – platelet interaction  Carboxylated prothrombin contains two carboxylate groups (COO – )  These groups bind to Ca 2+ forming prothrombin-calcium complex  The complex then binds to phosholipids on the surface of platelets (important for blood clotting)  Converting prothrombin to thrombin and initiating clot formation

14 Functions of Vitamin K Synthesis of  -carboxyglutamate in osteocalcin  Osteocalcin is a bone protein  May have a role in bone formation and mineralization   -carboxyglutamate is required for osteocalcin binding to hydroxyapatite (a mineral) in the bone  The function of bone osteocalcin is unclear

15 Deficiency of Vitamin K Deficiencies are rare: it is synthesized by the intestinal bacteria Hypoprothrombinemia: increased blood coagulation time May affect bone growth and mineralization Malabsorption of lipids leads to vitamin K deficiency

16 Deficiency of Vitamin K Prolonged antibiotic therapy Gastrointestinal infections with diarrhea  Both of the above destroy the bacterial flora leading to vitamin K deficiency Deficiency most common in newborn infants  Newborns lack intestinal flora  Human milk cannot provide enough vitamin K  Supplements are given by injection

17 Clinical Manifestations of the Deficiency Hemorrhagic disease of the newborn Bruising tendency, ecchymotic patches (bleeding underneath the skin) Mucus membrane hemorrhage Post-traumatic bleeding / internal bleeding Prolonged prothrombin time

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