Vitamin K and Blood Coagulation

Vitamin K Overview - K's Chemical Kingdom

• Fat-soluble vitamin, essential for blood coagulation.
• Naphthoquinone derivatives.
• Types:
  • K1 (Phylloquinone): Dietary; from green leafy vegetables (e.g., spinach, kale).
  • K2 (Menaquinone): Synthesized by intestinal flora (e.g., E. coli).
  • K3 (Menadione): Synthetic, water-soluble pro-vitamin; can be toxic in high doses.
• Core structure: 2-methyl-1,4-naphthoquinone ring.

⭐ Vitamin K1 (phylloquinone) is the primary dietary source, obtained from green leafy vegetables, while Vitamin K2 (menaquinone) is predominantly synthesized by bacteria in the gut.

• Deficiency leads to bleeding disorders due to impaired synthesis of clotting factors II, VII, IX, X, Protein C & S. (📌 Koagulation vitamin; Factors 2, 7, 9, 10 + C, S - think 1972 + CS).

Vitamin K Cycle & Action - The Gamma-Carboxylation Game

• Source & Active Form: Dietary Vitamin K (K1-phylloquinone, K2-menaquinone) is reduced to active Vitamin K hydroquinone (KH2).
• Key Enzyme: Hepatic $\gamma$-glutamyl carboxylase (GGCX).
  • Requires cofactors: KH2, O2, CO2.
  • Catalyzes: Post-translational carboxylation of Glutamate (Glu) residues $\rightarrow$ $\gamma$-carboxyglutamate (Gla) residues.
• Gla's Role: Gla residues on specific proteins create Ca²⁺ binding sites, essential for their biological activity.
  • Proteins involved: Clotting Factors II, VII, IX, X; Anticoagulant Proteins C, S, Z.
• Vitamin K Cycle:

• 

⭐ Warfarin, an oral anticoagulant, primarily inhibits Vitamin K epoxide reductase (VKORC1), thus blocking the regeneration of active Vitamin K hydroquinone (KH2) and impairing synthesis of functional clotting factors.

• 📌 Gla-Proteins: Clotting Factors II, VII, IX, X. Anticoagulants: Protein C, Protein S, Protein Z.

Clotting Factors & Cascade - K's Coagulation Crew

• Vitamin K-Dependent Factors: Essential for hemostasis.
  • Pro-coagulants: Factors II (Prothrombin), VII, IX, X. Synthesized in liver.
  • Anti-coagulants: Protein C, Protein S.
  • 📌 Mnemonic: Factors II, VII, IX, X = "1972" (X=10, IX=9, VII=7, II=2). Also Protein C & S.
• Mechanism: Post-translational modification.
  • Vitamin K is a cofactor for hepatic enzyme $\gamma$-glutamyl carboxylase.
  • This enzyme carboxylates glutamate (Glu) residues $\rightarrow$ $\gamma$-carboxyglutamate (Gla) on precursor proteins.
  • Gla residues are strong $Ca^{2+}$ chelators, enabling factors to bind phospholipid surfaces (e.g., activated platelets) and participate in cascade.

⭐ Factor VII has the shortest half-life among Vitamin K-dependent factors, making PT an early indicator of Vitamin K deficiency or warfarin effect.

Deficiency, Diagnosis & Uses - K's Clinical Corner

High‑Yield Points - ⚡ Biggest Takeaways

• Vitamin K is crucial for γ-carboxylation of glutamate residues in clotting factors.
• Activates factors II, VII, IX, X and anticoagulant proteins C & S.
• Warfarin acts by inhibiting vitamin K epoxide reductase, preventing Vitamin K recycling.
• Hemorrhagic disease of the newborn is due to Vitamin K deficiency.
• Key dietary sources include green leafy vegetables (K1); synthesized by gut flora (K2).
• Deficiency results in ↑Prothrombin Time (PT) and ↑INR.
• γ-carboxylation of clotting factors primarily occurs in the liver.