# Vitamin K Biochemistry

**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](/content/view/4025/index.html) 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](/content/browse#playlist-2700/index.html) among Pixorize's visual mnemonics for the USMLE Step 1 and NBME shelf exams.