KiskunlachÃ¡za

The vitamin K is a Vitamine Liposoluble (i.e. soluble in the Lipide S, but insoluble in water), synthesized by the Bactérie S of the intestinal Flora, and intervening in the synthesis of factors of blood Coagulation and the fixing of the Calcium by the bones.

One distinguishes two types of vitamin K: the vitamin K1 (phylloquinone-coming from a vegetable synthesis) and the vitamin K2 (ménaquinone-resulting from a bacterial synthesis) from which the structures and the actions are different.

The term Vitamine K is sometimes used to indicate the Kétamine, a product Psychotrope having nothing to do with this vitamin.

Discovered

Towards the end of the year 1920, a biochemist Danish, Carl Peter Henrik Prejudice, studies the role of the Cholestérol by nourishing Poulet S with a food low in Lipide S. It notes that after several weeks of Régime, these animals suffer from Hémorragie S, not disappearing, even after cholesterol addition in their food. It appears clear that in addition to cholesterol, another substance, for coagulant purpose, was withdrawn from food. This compound is called vitamin of coagulation and receives the letter K (the discovery was published in German, language in which the molecule was indicated like K oagulations Vitamin).

In 1936, Dam manages to purify the vitamin K starting from the Luzerne, and its chemical synthesis is carried out in 1939 by Edward Doisy. These two scientific divided the Nobel Prize of medicine in 1943 for their work on the vitamin K.

Physiology

The vitamin K is implied in the carboxylation of certain proteinic glutamate residues to form residues of Gamma-carboxyglutamate. The residues of gamma-carboxyglutamate are implied in the fixing of calcium and are essential for the biological activity of all the known proteins gamma-carboxyglutamate.

Currently, 14 proteins gamma-carboxyglutamate were discovered and they play a part in the regulation of three physiological processes:

coagulation
metabolism of the bones
vascular biology

Several bacteria whose Escherichia coli present in the large intestine can synthesize the vitamin K2 (menaquinone), but not the K1 vitamin.

Roles

The K1 vitamin plays an essential part in the blood Coagulation, it intervenes in the maturation of the factors:

of the endogenous way: factor IX;
of the exogenic way: factor (VII);
of the joint base: factors II) and X.

The liver produces these factors in an inactive form. Their maturation is ensured by an enzyme (the vitamin K carboxylase) whose cofactor is hydroquinone, the reduced shape of the K1 vitamin. The glutamic residues (Lime) of the Protéine S are then carboxyls in acids gamma-carboxyglutamiques (Gla) which have the property to fix calcium, essential to their activity. Same manner, vitamin K₂ allows the fixing of calcium (in the form of Hydroxyapatite) on the Ostéocalcine, a protein constitutive of the Os.

The drugs Anti-vitamin K (used among patients presenting a risk of Thrombosis) prevent the intestinal absorption of the vitamin K.

The vitamin K is necessary for the manufacture of Protéine S which plays a part in the Coagulation of blood (as much in stimulation that the Inhibition blood coagulation). It also takes part in the formation of the Os. In addition to being in the food, the Vitamine K is manufactured by the Bactérie S present in the Intestin, from where the scarcity of the Carence S in this Vitamine.

Contributions

The K1 vitamin, which takes part in coagulation, is brought by the food. One finds it in particular in the Légume S greens (Brocoli, cabbage, spinach, Laitue) and in the oil of Soja.

Most of the contributions in vitamin K₂, which takes part in the Ossification, is ensured by the Bactérie S of the intestinal Flora. This vitamin is also present in the Foie, the Lait, the Fromage, the Yogourt and oils of Poisson.

The requirements in vitamin K, about 45 µg/jour in the adult, are very largely met by the food and secretion for the flora saprophyte.

Structure

Simple: Vitamin K Zh-min-nan: Bi-tá-mín K

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