Vitamin K

Question 1

Vitamin K1, aka. ____(a)____ is found in green plant leaves; a related form, Vitamin K2, aka.____(b)____ is formed by bacteria living in the vertebrate intestine.

Answer 1

(a) phylloquinone
(b) menaquinone

Question 2

What are the roles of Vitamin K?

Answer 2

~ It is essential for the synthesis of prothrombin and several other clotting factors. [The vitamin K-dependent carboxylation reaction converts glutamate, a weak chelator of Ca2+ into γ-carboxyglutamate, a much stronger chelator. Prothrombin is thus able to bind Ca2+. Several coagulation factors (II, VII, IX and X) require posttranslational modification of glutamate residues to γ-carboxyglutamate.]
~ The enzyme γ-glutamyl carboxylase requires reduced vitamin K as a cosubstrate and converts it to an epoxide. The latter is reduced again by vitamin K epoxide reductase, which is inhibited by the drug warfarin.
~ Dicoumarol is used clinically as an anticoagulant to prevent thromboses in patients prone to clot formation. Dicoumarol and such related vitamin K antagonists as warfarin also serve as effective rat poisons.

Further notes:
Chelation is a type of bonding of ions and molecules to metal ions.

Question 3

What are effects of Vitamin K deficiency?

Answer 3

~ Insufficient carboxylation of glutamate in prothrombin, a clotting protein, slows blood clotting and can lead to hemorrhage.
~ In infants this can cause hemorrhagic disease of the newborn.

Question 4

List the coagulation/clotting factors that require post translational modification of glutamate residues to γ-carboxyglutamate for it to function.

Answer 4

Factor II: Prothrombin
Factor VII: Proconvertin
Factor IX: Christmas factor (a zymogen of serine protease)
Factor X: Stuart’s factor or Prower’s factor