| Vitamin K2 or menaquinone (MK) () is one of three types of vitamin K, the other two being vitamin K1 (phylloquinone) and K3 (menadione). K2 is both a tissue and bacterial product (derived from vitamin K1 in both cases) and is usually found in animal products or fermented foods.
The number n of isoprenyl units in their side chain differs and ranges from 4 to 13, hence vitamin K2 consists of various forms. It is indicated as a suffix (-n), e. g. MK-7 or MK-9. The most common in the human diet is the short-chain, water-soluble menatetrenone (MK-4), which is usually produced by tissue and/or bacterial conversion of vitamin K1, and is commonly found in animal products. It is known that production of MK-4 from dietary plant vitamin K1 can be accomplished by animal tissues alone, as it proceeds in germ-free rodents.
However, at least one published study concluded that "MK-4 present in food does not contribute to the vitamin K status as measured by serum vitamin K levels. MK-7, however significantly increases serum MK-7 levels and therefore may be of particular importance for extrahepatic tissues."
Long-chain menaquinones (longer than MK-4) include MK-7, MK-8 and MK-9 and are more predominant in fermented foods such as natto and cheonggukjang. Longer-chain menaquinones (MK-10 to MK-13) are produced by anaerobic bacteria in the colon, but they are not well absorbed at this level and have little physiological impact.
When there are no isoprenyl side chain units, the remaining molecule is vitamin K3. This is usually made synthetically, and is used in animal feed. It was formerly given to premature infants, but due to inadvertent toxicity in the form of hemolytic anemia and jaundice, it is no longer used for this purpose. K3 is now known to be a circulating intermediate in the animal production of MK-4. |
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Escherichia coli
(NCBI:txid562)
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See:
PubMed
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Escherichia coli metabolite
Any bacterial metabolite produced during a metabolic reaction in Escherichia coli.
mouse metabolite
Any mammalian metabolite produced during a metabolic reaction in a mouse (Mus musculus).
(via vitamin K )
fat-soluble vitamin (role)
Any vitamin that dissolves in fats and are stored in body tissues. Unlike the water-soluble vitamins, they are stored in the body for long periods of time and generally pose a greater risk for toxicity when consumed in excess.
(via vitamin K )
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View more via ChEBI Ontology
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a menaquinone
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UniProt
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Menaquinone
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KEGG COMPOUND
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menaquinone-n
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ChEBI
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Menatetrenone
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KEGG COMPOUND
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MK-n
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ChEBI
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vitamin K2
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ChemIDplus
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11032-49-8
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CAS Registry Number
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ChemIDplus
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