Vitamin K

Question 1

Where is Vitamin K1 synthesized vs 2? How will their structures differ?

Answer 1

Vitamin K1 = phylloquinone

• synthesized in PLANTS

Vitamin K2= menaquinone

• synthesized in BACTERIA

Question 2

Name two antivitamin K compounds.

Answer 2

Dicoumarol (a product of coumarin catabolism) and warfarin (anticoagulant, rat poison) are anti-vitamin K compounds.

Trick: Coumadin (like coumarin) is the generic name for warfarin.

Question 3

Function of Vitamin K

Answer 3

Carboxylation of glutamic acid residues in certain proteins, such as Ca2+ binding proteins.

• happens post translationally

Question 4

Reduced vitamin K (dihydrovitamin K) acts as a cofactor for what enzyme? Where does this enzyme act?

Answer 4

• Vitamin K-dependent carboxylase
• ER in the liver

Question 5

Which clotting factors are are affected by Vitamin K?

Answer 5

II, VII, IX and X are converted to y-caroxyglutamate residues.

Some bonus info: Prothrombin is also affected by Vitamin K’s carbxoylation of glutamic residues.

Remember: Ca2+ also plays a role in clotting.

Question 6

What unlikely source produces Vitamin K? What are the consequences of this?

Answer 6

Gut microflora produces Vitamin K. 90% of Vitamin K in liver is menaquinone (aka the K2 form produced by bacteria).

As such, antibiotics may DECREASE blood’s ability to clot.

Newborns are also prone to deficiency of vitamin K because absorption across placent is minimal and breast milk is low in Vitamin K. Newborns also do not have gut microflora.

Question 7

Why does defiency in Vitamin K cause bone disorders?

Answer 7

Vitamin K works to y-carboxylate glutamic acid residues of calcium binding proteins, such as calbindin