(Jrt)
Vitamin K
Vitamin K is a fat-soluble vitamin (ie soluble in fat, but insoluble in water), synthesized by the bacteria in the gut flora, and involved in the synthesis of blood clotting factors and fixing calcium by the bones.
There are two types of vitamin K: vitamin K1 (phylloquinone-from a synthesis plant) and vitamin K2 (ménaquinone-resulting from a bacterial synthesis), whose structures and actions are different.
The term Vitamin K is sometimes used to refer ketamine, a psychotropic product has nothing to do with this vitamin।
Discovery
Towards the end of 1920, a Danish biochemist, Peter Carl Henrik Dam, studies the role of cholesterol in feeding chickens with a diet low in fat. He noted that after several weeks of the regime, these animals suffer from haemorrhage, does not disappear, even after the addition of cholesterol in their diets. It is clear that more cholesterol, another substance, a coagulant effect was removed from the food. This compound is called coagulation of the vitamin and receives the letter K (the discovery was published in German, the language in which the molecule was identified as Koagulations Vitamin).
In 1936, Dam manages to purify vitamin K from alfalfa, and its chemical synthesis is conducted in 1939 by Edward Doisy. These two scientists shared the Nobel Prize for medicine in 1943 for their work on vitamin K.
Physiology
Vitamin K is involved in the carboxylation of certain residues protéïques of glutamates to form a residue of gamma-carboxyglutamate. The residues of gamma-carboxyglutamate are involved in setting the calcium and are essential for biological activity of all proteins gamma-carboxyglutamate known.
Currently, 14 gamma-carboxyglutamate proteins have been discovered and they play a role in the regulation of three physiological processes:
* The coagulation
* The bone metabolism
* The vascular biology
Several bacteria including Escherichia coli present in the large intestine can synthesize vitamin K2 (menaquinone), but not vitamin K1.
Roles
The vitamin K1 plays an indispensable role in blood clotting, it intervenes in the maturation of factors:
* Towards endogenous factor IX;
* Track exogenous factor (VII);
* Core factors II) and X.
The liver produces these factors in an inactive form. Their maturation is provided by an enzyme (vitamin K carboxylase) whose cofactor is hydroquinone, the reduced form of vitamin K1. Residues glutamic (Glu) proteins are then carboxylés acid-gama carboxyglutamiques (Gla) having ownership to fix calcium, essential for their activity. In the same way, vitamin K2 allows the fixing of calcium (in the form of hydroxyapatite) on osteocalcin, a protein constituent of bone.
The anti-vitamin K (used in patients with a risk of thrombosis) prevent the regeneration of vitamin K (2 this by inhibiting enzymes that régénerent vitamin K: epoxide reductase and NADPH-quinone reductase). Vitamin K is necessary for the manufacture of proteins that play a role in blood clotting (both in the stimulation that the inhibition of blood clotting). It also participates in the formation of bone. In addition to find in food, vitamin K is produced by bacteria in the intestine, hence the scarcity of this vitamin deficiencies.
Assets
The vitamin K1, which is involved in clotting, is provided by food. They are found especially in green vegetables (broccoli, cabbage, spinach, lettuce) and soybean oil.
Much of vitamin K2, which participates in the ossification, is ensured by the bacteria in the gut flora. This vitamin is also present in the liver, milk, cheese, yogurt and fish oils.
The need for vitamin K, around 45 μ g / day in adults, are widely covered by the Food and secretion of flora saprophyte.
Read also Vitamin A
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