Vitamin K is a group name for a number of related compounds,
which have in common a methylated naphthoquinone ring structure
(see figure 1), and which vary in the aliphatic side chain
attached at the 3-position.
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Figure 1: Menadione (K 3) |
Phylloquinone (also known as vitamin K1)
invariably contains in its side chain four isoprenid residues one
of which is unsaturated (figure 2).
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|
Figure 2: 2D structure of vitamin K1 |
3D structure of vitamin K1
Designed by Dr. G Nicolaes |
Menaquinones (known as vitamin K2) 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
(Figure 3).
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|
Figure 2: 2D structure of vitamin K2
n stands for the number of
isoprenoid residues
|
3D structure of Menaquinone-7
Designed by Dr. G Nicolaes |
It is generally accepted that the naphthoquinone is the functional
group, so that the mechanism of action is similar for all K-vitamins.
Substantial differences may be expected, however, with respect to
intestinal absorption, transport, tissue distribution, and bio-availability.
These differences are caused by the different lipophilicity of the
various side chains, and by the different food matrices in which
they occur. |
