Vitamin K is a name given to a group of derivatives of 2-methyl-1,4-naphthoquinone that are required by mammals for the posttranslational modification of certain proteins, mostly involved in blood coagulation. These compounds, while essential for mammals, are not synthesized by them, and are thus considered vitamins.
The natural forms of the vitamin are vitamin K1 (phylloquinone) and vitamin K2 (a menaquinone). Since menaquinones produced by different organisms have different tail lenghts, there are many variations of vitamin K2, usually specified based on the number of carbons in their tails, such as in Vitamin K2(45). Menaquinones are synthesized by gut bacteria, and are absorbed into the blood. Thus, dietary deficiency is extremely rare in healthy individuals.
There are also several synthetic forms- vitamin K3 through K9. Vitamin K3 (menadione) is the most active of the synthetic forms.
Child Classes: a menaquinone (17)
Unification Links: Wikipedia:Vitamin_k
Fujimoto12: Fujimoto N., Kosaka T., Yamada M. (2012). "Menaquinone as Well as Ubiquinone as a Crucial Component in the Escherichia coli Respiratory Chain." Chapter 10 in Chemical Biology, edited by D Ekinci, ISBN 978-953-51-0049-2.
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