Vitamin K is a fat-soluble vitamin that acts as a coenzyme in the coagulation process. It exists in three forms: K1 from plants, K2 from intestinal bacteria and animals, and K3 which is synthetic. Vitamin K is important for the carboxylation of clotting factors II, VII, IX, X and proteins C and S in the liver. This carboxylation adds a negative charge that allows the clotting factors to bind to platelet membranes and interact efficiently to form blood clots. Vitamin K deficiency can result from fat malabsorption, broad-spectrum antibiotics that kill gut bacteria, or excessive loss of vitamin K in the feces, leading to bleeding disorders
2. Introduction
Ć¼Water soluble vit has many coenzyme fxn, BUT Vit KĆ only fat soluble
vit with coenzyme.
Ć¼Has role in coagulation process.
Ć¼Exist in 3 different form:
ā¢ Vit. K1( phylloquinone): plant, green veg.
ā¢ Vit K2( menaquinone): intestinal bacteria & animal.
ā¢ Vit K3( menadione): is a synthetic formĆ can be metabolized to
phylloquinone.
3. Furtherā¦ā¦ā¦.
ā¢ Isoprenoid unit is present ( K1 and K2)
ā¢ Stable to heat.
Dietary sources:
Good sources: Cabbage, cauliflower,
tomatoes, spinach & green vegetables.
Also +nt: egg yolk , meat , liver, cheese
& milk products.
4. Absorption, transport and storage
ā¢ Diet or intestinal bacteriaĆ vit K
ā¢ Absorption is taken place in +nce of chylomicrons & bile salts.
ā¢ Transported along with LDL & stored in liver.
ā¢ Little in other tissue.
RDA: Strictly speaking Ć no RDA, since it can be synthesized in GUT
by flora.
However, recommended ( Ā½ by diet & Ā½ by bacterial flora)
AccordinglyĆ suggested Ć RDA: 70-140 šg/day.
5. Function: mainly in clotting process
ā¢ Post translational modification of II, VII, IX, X & protein C and S
zymogens ( inactive precursors)Ć activeĆ coagulation process.
ā¢ Modification: acts as COENZYME for the carboxylation of glutamate aa of
above factors Ć Ī³-carboxyglutamate (Gla)Ć which chelates the calcium
ionĆ binds to platelet membrane
ā¢ Vit k dependent factors: II, VII, IX ,X AND Protein C& S.
ā¢ Also require for carboxylation of osteocalcin Ć calcium binding protein in
bone
6. Role of Gla in clotting
ā¢ Ī³-carboxyglutamate (Gla) Ć neg charge (coo-).
ā¢ Binds with +ve ca++, which in turn binds with phospholipids (-ve) on
membrane surface of platelets.
ā¢ Brings the clotting factor together Ć more interaction betwn themĆ
action become more efficient on platelets platform
7.
8. ā¢ Dicumarol ( natural) & warfarin ( synthetic)Ć reduce blood clot.
ā¢ After carboxylation, vit k ( HQ) is converted Ć 2,3 epoxide form
ā¢ Which is converted by epoxide reductase Ć to Quinone
ā¢ Quinone by another reductase Ć to vit K(HQ) again to become active
ā¢ Dicumarol & warfarinĆ inhibits epoxide reductase.
Antagonist of vit K
ā¢ deep vein thrombosis,
ā¢ pulmonary embolism,
ā¢ heart attack,
ā¢ stroke
9. A high dose of vit K is the antidote to an
overdose of warfarin
ā¢ If enough vitamin K (a quinone) is givenĆ by diet,
ā¢ Get reduced to the active hydroquinone by the warfarin-
insensitive enzyme, and carboxylation can continue,
10. Deficiency symptoms
Ć¼Causes
ā¢ Fat malabsorption
ā¢ āā broad-spectrum antibiotics ( killing of gut flora)
ā¢ Loss of vit. K in feces (diarrhea)
Ć¼Leads to ( āā active prothrombin)
ā¢ Bleeding disordersĆ profusely bleeds even for minor injury.
Ć¼Hypervitaminosis: āā RBC destructionĆ
anemia & jaundice