How many isoforms of vitamin K are there?

By William Aird

The vitamin K family is comprised of multiple similarly structured fat-soluble molecules containing a 2-methyl-1,4-naphthoquinone ring structure called menadione. There are three main structures of vitamin K:

  • Natural occurring:
    • Phylloquinone (K1)
      • The predominant form of vitamin K present in the diet.
      • Predominantly found in green vegetables and plant chlorophylls.
      • Used to treat patients with vitamin K deficiency or to reverse vitamin K antagonists.
    • Menaquinones (K2)
      • Further subdivided into:
        • Short-chain (e.g., menaquinone-4; MK-4)
        • Long-chain (e.g.,, MK-7, MK-8, and MK-9)
      • Synthesized by bacteria.
      • Primarily found in food where bacteria are part of the production process.
  • Synthetic origin:
    • Menadione (K3)
    • Converted into K2 in liver.
    • Harmful effects shown in humans, therefore not used therapeutically.

Both vitamin K1 and K2 can function as cofactors in the carboxylation process of vitamin K-dependent proteins.

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