-Chinmay Kumar Sahoo
Introduction-
Vitamins were first discovered by N.L Lunin and named ‘vitamin’ by Funk. There are eight vitamin B complexes. Vitamin B12, also known as cobalamin, is a water-soluble, antioxidant vitamin involved in metabolism and is one of those eight. There are two metabolically active forms of vitamin B-12 namely Methylcobalamin and 5-deoxyadenosylcobalamin. However, two other forms, hydroxocobalamin and cyanocobalamin, become biologically active after they are converted to methylcobalamin or 5-deoxyadenosylcobalamin. Some good sources of vitamin B-12 include-meat, fish, milk, cheese, eggs, and some fortified breakfast cereals.
Chemistry-
Vitamin B12 has the most complex structure of all vitamins. It was elucidated by Nobel Laureate and crystallography pioneer Dorothy Crowfoot Hodgkin. It has a formula -C63H88CoN14O14P and an IUPAC name-α-(5,6- Dimethylbenzimidazole) cobinamide cyanide. The structure of B12 is made up of a corrin ring. The central metal ion is cobalt. In vitamin B12 cobalt is present in its +3oxidation state. Biochemically, the cobalt center can take part in both two-electron and one-electron states. The ability to shuttle between the +1, +2, and +3 oxidation states is responsible for the versatile chemistry of vitamin B12. Out of six coordination sites four sites are provided by the corrin ring, and the fifth by a dimethylbenzimidazole group. The sixth coordination site or the reactive center is a variable site, it can have groups like cyano group (–CN), a hydroxyl group (–OH), a methyl group (–CH3) or a 5′-deoxyadenosyl group respectively.
The presence of vitamin B12 in food can be determined by several methods like microbiological assays, chemiluminescence assays, polarographic, spectrophotometric and high-performance liquid chromatography.
Function of B12-
Vitamin B12 functions as a coenzyme, that means its presence is required for enzyme-catalyst reaction. The classes of enzymes which require B12 for proper functioning are isomerase, methyltransferases and dehalogenase. Vitamin B12 functions as a cofactor for two enzymes, methionine synthase and L-methylmalonyl-CoA mutase. Methionine synthase catalyzes the conversion of homocysteine to the essential amino acid methionine. Methionine is required for the formation of S-adenosylmethionine, a universal methyl donor for almost 100 different substrates, including DNA, RNA, proteins, and lipids. L-methylmalonyl-CoA mutase converts L-methylmalonyl-CoA to succinyl-CoA in the metabolism of propionate, a short-chain fatty acid. It is a cofactor in DNA synthesis, in both fatty acid and amino acid metabolism. It is important in the normal functioning of the nervous system via its role in the synthesis of myelin, and in the maturation of red blood cells in the bone marrow.
Deficiency-
Vitamin B12 deficiency can potentially cause severe and irreversible damage, especially to the brain and nervous system. Pernicious anemia (PA) is a type of vitamin B12 deficiency anemia. It is a disease in which not enough red blood cells are produced due to a deficiency of vitamin B12. Other causes of low vitamin B12 include celiac disease, or tapeworm infection.
