Vitamin K (K from "Koagulations-Vitamin" in German, Danish, Swedish and Norwegian
[1]) denotes a group of
lipophilic,
hydrophobic vitamins that are needed for the
posttranslational modification of certain proteins, mostly required for
blood coagulation. Chemically they are 2-
methyl-
1,4-naphthoquinone derivatives.
Vitamin K2 (menaquinone, menatetrenone) is normally produced by bacteria in the intestines, and dietary deficiency is extremely rare unless the intestines are heavily damaged or are unable to absorb the molecule[citation needed].
All members of the vitamin K group of vitamins share a methylated naphthoquinone ring structure, and vary in the aliphatic side chain attached at the 3-position (see figure 1). Phylloquinone (also known as vitamin K1) invariably contains in its side chain four isoprenoid residues, one of which is unsaturated.
Menaquinones have side chains composed of a variable number of unsaturated isoprenoid residues; generally they are designated as MK-n, where n specifies the number of isoprenoids.
