Vitamin B-12 or B12.A vitamin synthesized by microorganisms and conserved in animals in the liver. Deficiency or collective uptake of vitamin B-12 leads to pernicious anemia. Cobalamin is a substituted corrin-Co(III) complex in which the cobalt atom is bound to the four nitrogen atoms of the corrin ring, an axial group R and 5,6-dimethylbenzimidazole.The latter is linked to the cobalt by the N-3 nitrogen atom and is bound to the C-1 carbon of a ribose molecule by the N-1 nitrogen atom. Various forms of the vitamin are known with different R groups such as R = CN, cyanocobalamin; R = OH, hydroxocobalamin; R = CH3, methylcobalamin; R = adenosyl, coenzyme B-12.
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