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introduction to Vitamin K
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introduction to vitamin k their sources, types of vitamin k, biochemical role, deficiency of vitamin k
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VITAMIN KINTRODUCTION:
The letter “K” is the abbreviation of the German word “koagulation vitamin”. All vitamin K
forms are the naphthoquinone or derivatives. with a long isoprenoid side chain. The length of
side chain will differ. Vitamin K1 has 20-Carbon side chain (phylloquinone). It is closely related to
a compound pthiocol, a constituent of tubercle bacilli with slight vitamin K activity..
SOURCES:
Both vitamin K1 and K2 are mainly found in plants and synthesised by bacteria
respectively. Vitamin K1 is present in green vegetables, such as alfalfa, spinach, cauliflower,
cabbage, soyabeans, tomatoes. Vitamin K2 also called Menaquinones is a product of
metabolism by the normal intestinal (gram positive) bacteria of most higher animal species.
.
NUTRITIONAL REQUIREMENTS:
The adequate intake for vitamin K is 120 mg/day for adult males and 90 mg for females.
ABSORPTION:
Absorption of vitamin K occurs in the intestine along with chylomicrons. Bile salts are required
for the normal absorption. The vitamin K may be derived from the diet or intestinal bacterial
synthesis. It is stored in the liver and transported in plasma along with beta lipoproteins.
Types of Vitamin K:
Vitamin K exists in several forms, for example, in plants as phylloquinone (or vitamin K1),
and in intestinal bacterial flora as menaquinone (or vitamin K2). A synthetic form of vitamin K,
menadione, is able to be converted to K2. Vitamins K1 and K2 are the two naturally occurring
forms of vitamin K that have been identified. The third form vitamin K3 is the synthetic analogue
, of K2. It is water soluble synthetic vitamin, widely used in clinical practice. Henrik Dam isolated
vitamin K1 in 1929, while Edward Doisy isolated vitamin K2 in 1939. Both of them were awarded
Nobel prize in 1943
1. Vitamin K1
It is phylloquinone or phytonadione isolated from alfalfa leaves. Also called Mephyton.
Thus vitamin K1 is 2 methyl, 3 phytyl-1,4 naphthoquinone. It is a light yellow oil
.
2. Vitamin K2
Also known as farnoquinone, it was isolated from putrid fish meal synthesised by bacteria..
Vitamin K2 (farnoquinone) is 2 methyl-3-difarnesyl-1,4 naphthoquinone. It is also a yellow oil.
3. Vitamin K3
Vitamin K3 is 2 methyl, 1, 4 naphthoquinone without any side chain or -OH group (Also known
as menadione), is the synthetic analogue of vitamin K. It is three times more potent than
natural varieties. It is water-soluble. Its activity is related to the presence of methyl group
at position 2. Other two forms are Menadiol and Menadioldiacetate.
Biochemical Role of Vitamin K
The principal role of vitamin K is in the post-translational modification of a number of proteins
(most of which are involved with blood clotting), in which it serves as a coenzyme in the
carboxylation of certain glutamic acid residues present in these proteins.
Blood coagulation:
The main function of vitamin K is the promotion of blood coagulation by helping in the
post-transcriptional modifications of blood factors such as prothrombin, and factors II,
VII, IX, X. Vitamin K is first converted to its hydroquinone form in liver microsomes by
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