VITAMIN B 12
It is also known as Anti-pernicious anemia vitamin.
It is a unique vitamin synthesized by only microorganisms and not by animals and plants.
CHEMISTRY-
The empirical formula of vitamin B12( cyanocobalamin) is C63H90N14O14PCo.
The structure of vitamin B12 consist of corrin ring with a central cobalt atom.
There are 2 coenzyme forms of vitamin B12
a) Methyl cobalamin
In which cyanide is replaced by methyl group.
b) 5-Deoxyadenosyl cobalamin-
Cyanide is replaced by 5 deoxyadenosine forming an unusual carbon cobalt bond.
ABSORPTION, TRANSPORT AND STORAGE-
The vitamin B12 is present in the diet in a bound form to proteins. B12 is liberated by the enzymes ( acid hydrolases) in the stomach. The dietary source of B12 is known as extrinsic factor of castle. The stomach secretes a special protein called intrinsic factor (IF). The cobalamin -IF complex travels through the gut. The complex binds to specific receptors on the surface of the mucosal cells of the ileum. The binding of the complex and entry of B12 into the mucosal cell is mediated by ca2+ ions. In the mucosal cells, B12 is converted to methylcobalamin. It is then transported in the circulation in a bound form to proteins namely transcobalamins. Methylcobalamin which is in excess is taken up by the liver, converted to deoxyadenosyl B12 and stored in this form. It is believed that liver can store about 4-5 mg, an amount sufficient to meet the body requirements of B12 for 4-6 years.
BIOCHEMICAL FUNCTIONS-
There are only 2 reactions in mammals that are dependent on vitamin B12-
1) Synthesis of methionine from homocysteine-
Vitamin B12 as methylcobalamin is used in this reaction.
2) Isomerization of methylmalonyl CoA to succinyl CoA-
The degradation of odd chain fatty acids, certain amino acids( valine, isoleucine etc) and pyrimidine (thymine and uracil) produce directly or through the mediation of propionyl CoA, an important compound methylmalonyl CoA. This is converted to succinyl CoA in the presence of B12 coenzyme, deoxyadenosyl cobalamin.
Recommended dietary allowance (RDA)
A daily intake of about 3 mg of vitamin B12 is adequate to meet the adult requirements. For children 0.5-1.5 mg/day is recommended. During pregnancy and lactation the requirement is 4 mg/day.
Dietary sources
Foods of animal origin are the only sources for vitamin B12. The rich sources are liver, kidney, milk, curd, eggs, fish, pork and chicken.
Curd is better source than milk due to synthesis of B12 by lactobacillus.
Vitamin B12 is synthesized only by microorganisms (anaerobic bacteria). Plants cannot synthesize, hence B12 is never found in plant foods. Animals obtain B12 either by eating foods, derived from other animals or from the intestinal bacteria synthesis.
Deficiency symptoms
The most important disease associated with vitamin B12 deficiency is pernicious anemia.
It is characterized by low hemoglobin levels, decreased number of erythrocytes and neurological manifestation.
The excretion of methylmalonic acid( elevated) in urine snd estimation of serum B12 level are used to assess B12 deficiency.
TREATMENT-
Vitamin B12 is administered in therapeutic dose ( 100-1000mg) intramuscularly. Folic acid administration can also reverse hematological abnormalities Obsevered in B12 deficiency. However, the neurological symptoms persist. Therfore a combined supplementation of B12 and folate is employed to treat the patient with megaloblastic anemia.
Role of vitamin B12 in COVID-19
Can vitamin B12 be an adjuvant to COVID-19 Treatment???
A recent study in Singapore has found that combination of vitamin D, magnesium and vitamin B12 could reduce the rate of progression
in older patients with COVID-19.
So, what is the outcome of role of vitamin B12 in COVID-19?
Vitamin B12 helps to maintain a healthy immune system, so it could potentially prevent COVID -19
Symptoms.
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