Vitamin B12

Vitamin B12 is also known as antipernicious anemia factor. This is a deep red, crystalline compound containing cobalt, cyanide and aminogroups in its molecular structure and that is why, it is also known as cyanocobalamin. It is soluble in water, stable to heat in neutral solution but is destroyed in dilute acidic or alkaline solutions. Its structure is very complex and has been worked out. It consists of porphyrinosimilar and nucleotidic parts (see figure). A molecule of vitamin B12 contains an atom of cobalt in the trivalent state. Vitamin B12 is known as cyanocobalamin. Other compounds of this type are also known – nitrocobalamin, aquacobalamin.

Sources the most important source of vitamin B12 is liver. Other but less important sources are milk, meat, eggs and fish. Vegetable foods generally lack these vitamins. Intestinal flora of microorganisms can also synthesize these vitamins. Their absorption requires the presence of an intrinsic factor which is found to be present in the normal gastric juice.

Functions vitamins B12 are essentially required for normal hematopoiesis (formation of blood) and erythrocyte maturation. In young animals these show a growth promoting effect. Similar growth effect is observed in young children. This vitamin increases the biosynthetic of nucleic acids, is involved in the metabolism of glycine, serine, methionine, choline and methyl groups, in the enzymic conversion of methylmalonyl CoA to succinyl CoA.

Vitamins B12 are clinically used in cases of megaloblastic anemia and to heat neurogical disturbances. Vitamin B12 are also required for the formation of myelin sheath in the nerves, and for activation of SH containing enzymes.

Deficiency symptoms

In the human subjects B12 deficiency rarely occurs, whenever it occurs, it causes perniciosa anemia. This deficiency usually occurs due to lack of a low molecular weight mucoprotein in the gastric juice, known as intrinsic factor. In the lack of this factor , vB12 (extrinsic factor), most probably helps in liberating B12 from natural protein – complexes and in their subsequent transport of blood. Intestinal juice is also known to secrete a factor which helps in the absorption of vB12 in collaboration to intrinsic factor. Intrinsic factor is also believed to help in the storage of B12 in the tissue, specially in the liver. B12 deficiency also leads to demylination of the nerves.

Requirement B12 requirement of the human beings not definitely known. Most probably 1,5mg B₁₂per day or even slightly lesser amount is adequate.

<== попередня сторінка	\|	наступна сторінка ==>
Thiamin, vB1, antinevrose	\|	Ascorbic acid (vitamin C)

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