Vitamin K2

General structure of vitamin K2 (MK-n)

Vitamin K2 or menaquinone (MK) (/ˌmɛnəˈkwɪnoʊn/) 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.[1]

The number n of isoprenyl units in their side chain differs and ranges from 4 to 13, hence vitamin K2 consists of various forms.[2] 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."[3]

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.[4] 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.[1]

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,[failed verification] it is no longer used for this purpose.[1] K3 is now known to be a circulating intermediate in the animal production of MK-4.[5]

  1. ^ a b c Myneni VD, Mezey E (November 2017). "Regulation of bone remodeling by vitamin K2". Oral Diseases. 23 (8): 1021–1028. doi:10.1111/odi.12624. PMC 5471136. PMID 27976475.
  2. ^ Mladěnka, Přemysl; Macáková, Kateřina; Kujovská Krčmová, Lenka; Javorská, Lenka; Mrštná, Kristýna; Carazo, Alejandro; Protti, Michele; Remião, Fernando; Nováková, Lucie (2022-03-10). "Vitamin K – sources, physiological role, kinetics, deficiency, detection, therapeutic use, and toxicity". Nutrition Reviews. 80 (4): 677–698. doi:10.1093/nutrit/nuab061. ISSN 1753-4887. PMC 8907489. PMID 34472618.
  3. ^ Sato T, Schurgers LJ, Uenishi K (November 2012). "Comparison of menaquinone-4 and menaquinone-7 bioavailability in healthy women". Nutrition Journal. 11 (93): 93. doi:10.1186/1475-2891-11-93. PMC 3502319. PMID 23140417.
  4. ^ Kang, Min-Ji; Baek, Kwang-Rim; Lee, Ye-Rim; Kim, Geun-Hyung; Seo, Seung-Oh (2022-03-03). "Production of Vitamin K by Wild-Type and Engineered Microorganisms". Microorganisms. 10 (3): 554. doi:10.3390/microorganisms10030554. ISSN 2076-2607. PMC 8954062. PMID 35336129.
  5. ^ Shearer, Martin J.; Newman, Paul (March 2014). "Recent trends in the metabolism and cell biology of vitamin K with special reference to vitamin K cycling and MK-4 biosynthesis". Journal of Lipid Research. 55 (3): 345–362. doi:10.1194/jlr.R045559. ISSN 0022-2275. PMC 3934721. PMID 24489112.