Vitamin K

Question 1

What are the chemical names for vitamin K1 and K2?

Answer 1

K1 = phylloquinone
K2 = menaquinone

Question 2

Name food sources for both Vitamin K1 and K2

Answer 2

K1 = plant form
dark leafy greens & natto (fermented soy beans)

K2 = bacterial forms
synthesized in the gut microbiota
found in meat and dairy products

Question 3

What is the primary function of vitamin K?

Answer 3

Coagulation via catalyzing the conversion of peptide bound glutamate to y-carboxylglutamyl.
(This conversion is essential for the biological activity of VKD proteins).

Question 4

What are the differences between the structures of K1 and K2?

Answer 4

There are 3 additional double bonds on the carbon side chain of K2 when compared to K1

Question 5

Name some vitamin K-dependent proteins (and what they do).

Answer 5

Protein C - anticoagulant role in the negative feedback control of coagulation
Protein S - anticoagulant role in the negative feedback control of coagulation
Osteocalcin - Gla protein that plays a role in bone and cardiovascular mineralization
Prothrombin

Question 6

How does Warfarin affect vitamin K status?

Answer 6

Warfarin is an antagonist to vitamin K and blocks VKOR activity which inhibits the recycling of vitamin K (this inhibits coagulation)

Question 7

Why is vitamin K thought to play an important role in bone health?

Answer 7

Osteocalcin (OC) = bone protein and biomarker for bone formation.
Vitamin K is an essential cofactor for the y-carboxylation of three glutamic acid residues in osteocalcin (decreased vitamin K = decreased carboxylation of osteocalcin)

undercarboxylation of osteocalcin in human bone and serum has been linked to vitamin K status

Question 8

Explain why vitamin K is given to newborns.

Answer 8

1. poor placental transfer
2. low vitamin K content in breast milk
3. poor intestinal absorption due to immature gut flora and malabsorption