pharmacology

2.  What is vitamin B12 ?
 Vitamin B12 is a powerhouse. It helps make DNA, nerve and
blood cells, and is crucial for a healthy brain and immune
system. Your metabolism wouldn't run smoothly without it. But
B12 isn't like other vitamins
 Chemical name of vitamin B12
 Vitamin B12; Cyanocobalamin;Cobalamin. Vitamin B12 is
a cobalt-containing coordination compound produced by
intestinal micro-organisms and found also in soil and water
 Source of vitamin B12
 The best sources of Vitamin B12 include: eggs, milk, cheese, milk
products, meat, fish, shellfish and poultry. Some soy and rice
beverages as well as soy based meat substitutes are fortified with
vitamin B12

3.  Structure
 B12 is the most chemically complex of all the vitamins. The
structure of B12 is based on a corrin ring, which is similar to
the porphyrin ring found in heme, chlorophyll and cytochrome.
The central metal ion is cobalt. Four of the six coordination sites
are provided by the corrin ring, and a fifth by a
dimethylbenzimidazole group. The sixth coordination site, the
center of reactivity, is variable, being a cyano group (-CN),
a hydroxylgroup (-OH), a methyl group (-CH3) or a 5'-
deoxyadenosyl group (here the C5' atom of the deoxyribose
forms the covalent bond with Co), respectively, to yield the four
B12 forms mentioned below. Historically, the covalent C-Co bond
is one of the first examples of carbon-metal bonds to be
discovered in biology. The hydrogenasesand, by necessity,
enzymes associated with cobalt utilization, involve metal-carbon
bonds.

5.  Mechanism of action
 Metabolism of folic acid. The role of Vitamin B12 is seen at bottom-left.
 Vitamin B12 functions as a coenzyme, meaning that its presence is required for
enzyme-catalyzed reactions.Three types of enzymes:
 Isomerases
 Rearrangements in which a hydrogen atom is directly transferred between two
adjacent atoms with concomitant exchange of the second substituent, X, which
may be a carbon atom with substituents, an oxygen atom of an alcohol, or an
amine. These use the adoB12 (adenosylcobalamin) form of the vitamin.
 Methyltransferases
 Methyl (-CH3) group transfers between two molecules. These use Me
B12 (methylcobalamin) form of the vitamin
 Dehalogenases
 Reactions in which a halogen atom is removed from an organic molecule.
Enzymes in this class have not been identified in humans.

7.  Vitamin B12 Deficiency
 Atrophic gastritis, in which your stomach lining has thinned
 Pernicious anaemia, which makes it hard for your body to absorb
vitamin B12
 Surgery that removed part of your stomach or small intestine,
including weight loss surgery
 Conditions affecting the small intestine, such as Crohn's disease
celiac disease, bacterial growth, or a parasite
 Heavy drinking
 Immune system disorders, such as Graves' disease or lupus
 Long-term use of acid-reducing drugs. Stomach acids help break
down animal proteins that have vitamin B12.

8.  Treatment for Vitamin B12 Deficiency.
 If you have pernicious anaemia or a problem with its absorption,
you'll need to replace vitamin B12 by injection initially and then
continued injections, high doses of an oral replacement, or nasal
therapy for life
 Daily for age B12
 Recommended dietary amounts (RDAs) are 2.4
micrograms daily for ages 14 years and older, 2.6
micrograms daily for pregnant females, and 2.8
micrograms daily for breastfeeding females. Those over 50 years
of age should meet the RDA by eating foods reinforced
with B12 or by taking a vitamin B12 supplement

9. Rokunuzzaman
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