Summary

Vitamin K is a fat-soluble vitamin synthesized by intestinal bacteria. Vitamin K is activated by the enzyme epoxide reductase to its reduced form, which acts as a cofactor for gamma-carboxylation of glutamic acid residues on blood clotting proteins. Therefore, Vitamin K plays an important role in coagulation (formation of blood clots), as there are a number of such vitamin K-dependent coagulation factors: including factors II, VII, IX, X, as well as protein C and S.

Key Points

• Vitamin K
  • Fat-soluble compounds synthesized by intestinal flora
    • Includes phytomenadione, phylloquinone, phytonadione
    • Vitamin K Deficiency typically caused by fat malabsorption
  • Activated by epoxide reductase to reduced form
    • Active Vitamin K is a cofactor for the y-carboxylation of glutamic acid residues needed to synthesize blood clotting factors
      • Vitamin K-dependent proteins include Factors II, VII, IX, X, proteins C and S
    • Warfarin (Coumadin) inhibits epoxide reductase, blocking vitamin K-mediated gamma-carboxylation

Find Vitamin K Biochemistry and other Vitamins among Pixorize's visual mnemonics for the USMLE Step 1 and NBME shelf exams.