Fat Soluble Vitamins: Vitamin K
Free online lectures on Vitamins by Biochemistry Club
- Vitamin K is a Fat Soluble Vitamin and is derivative of Naphthoquinone with a long Isoprenoid side chain.
- Vitamin K1 has 20C side chain (Phylloquinone)
- Vitamin K2 has 30C side chain (Menaquinone)
- Structurally similar synthetic compound is menadione.
- Vitamin K exists in several forms:
- Phylloquinone (Vit.K1) – present in plants.
- Menaquinone (Vit. K2) – present in intestinal bacterial flora.
- Menadione, menadiol & menadiol acetate are the synthetic derivatives.
- In intestine along with chylomicrons.
- Bile salts are required for normal absorption.
- May be derived from diet or intestinal bacterial synthesis.
- It is stored in liver
- Transported in plasma along with beta lipoproteins.
Biochemical Role of Vitamin K
- Vitamin K is necessary for coagulation.
- Vitamin K dependent factors in the coagulation pathway are Factor II (Prothrombin); Factor VII; Factor IX; Factor X
- All Factors are synthesized as inactive zymogens in the liver.
- These factors undergo posttranslational modification (gamma carboxylation of glutamic acid residues).
- These act as the binding sites for calcium ions.
- The Gamma carboxy glutamic acid (GCG) synthesis requires Vitamin K as a co-factor.
- Vitamin K dependent gamma carboxylation is also necessary for the functional activity of osteocalcin as well as structural proteins of kidney, lung and spleen.
- Osteocalcin (protein 40–50 amino acids length) is synthesized by osteoblasts and seen only in bone.
- Osteocalcin binds tightly to hydroxy apatite …
FOR FULL LESSON GO TO HOME PAGE, CLICK BIOCHEMISTRY I AND THEN CLICKVITAMINS. IN VITAMINS SECTION, CLICK CURRICULUM TO VIEW THE FULL LIST OF LESSONS .