Biochemistry of Vitamin K: Sources, Absorption and its Biochemical role

Fat Soluble Vitamins: Vitamin K

Free online lectures on Vitamins by Biochemistry Club

Introduction

• 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.

Sources

• Vitamin K exists in several forms:
  1. Phylloquinone (Vit.K1) – present in plants.
  2. Menaquinone (Vit. K2) – present in intestinal bacterial flora.
  3. Menadione, menadiol  & menadiol acetate are the synthetic derivatives.

Absorption

• 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 .