Introduction
K vitamin indicates a group of 2-methilo-naphthoquinone derivatives. They are human vitamins, lipopholic (i.e., soluble in lipids) and therefore hydrophobic (i.e., insoluble in water). They are required for the posttranslational modification of certain proteins, mostly required for blood coagulation. Normally k vitamin is produced by bacteria in the intestines and dietary deficiency is extremely rare unless the intestines are heavily damaged.
Chemical structure
K vitamin is a group name for a number of related compounds, which have in common a methylated naphthoquinone ring structure, and which vary in the aliphatic side chain attached at the 3-position. 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.
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.
Deficiencies of k vitamin
Some of the deficiencies of k vitamin are as follows:
Increased risk of fractures or reduced bone density may result from inadequate intake of vitamin K
Hemorrhagic disease of the newborn results from vitamin K deficiency in human infants.
Intestinal disease
Liver disease
Poisoning with vitamin K antagonists
Sources of K vitamin
K vitamin is found in a number of foods, including green leafy vegetables, cauliflower. However, the main source of vitamin K is synthesis by bacteria in the large intestine, and in most cases, absence of dietary vitamin K is not at all venomous. Vitamin K is a fat-soluble vitamin and both dietary and microbial vitamin K is absorbed into intestinal lymph along with other lipids. The fetus obtains vitamin K from its mother by transplacental transfer.
Conclusion
K vitamin serves as an essential cofactor for a carboxylase that catalyzes carboxylation of glutamic acid residues on k vitamin dependent proteins.

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