1. Adenosylcobalamin is the coenzyme involved with tetrahydrofolate in the synthesis of labile methyl groups which can be transferred to homocysteine to form methionine.

2. It is also a coenzyme for the conversion of methylmalonyl – CoA to succinyl-CoA. This is a key reaction in the pathway of conversion of propionate to a member of the citric acid cycle and is therefore of significance in the process of gluconeogenesis.

3. It is of particular importance in ruminants, since propionate is a major product of microbial fermentation in the rumen.

4. It plays important part in the production of nucleic acids and in the process of cell division in the body. It is required in the conversion of rionucleotides to deoxyribonucleotides.

5. Vitamin B₁₂ along with folic acid is required for the development of red blood cells beyond megaloblastic stage.

6. It is involved in the synthesis of protein. It stimulates the appetite and general health.

Deficiency Deficiency of vitamin B12 leads to megaloblastic anemia. When absorption is prevented by lack of intrinsic factor (or by gastrectomy), the condition is called pernicious anemia. Vegetarians are at risk of actual dietary deficiency, since the vitamin is found only in foods of animal origin or in microorganisms-so that foods contaminated with microorganisms are of benefit in that way.

The deficiency leads to impairment of the methionine synthase reaction. Anemia results from impaired DNA synthesis, preventing cell division and formation of the nucleus of new erythrocytes with megaloblasts. The impaired purine and pyrimidine synthesis resulting from tetrahydrofolate deficiency is a consequence of folate being trapped as methyltetrahydrofolate (known as the “folate trap’).

RDA

  Infants :0.3µg

 Children :1-2µg

 Adult (male) :3.0µg

 Adult (female) :3.0µg

 Pregnant women :4.0µg

 Lactating women :4.0µg 

Sources 

Richest sources : Liver, kidney

Good sources : Meat, fish, eggs

Fair sources : Milk, cheese.