generic descriptor for compounds exhibiting the biologic activity of cyanocobalamin; the antianemia factor of liver extract that contains cobalt, a cyano group, and corrin in a cobamide structure. Several substances with similar formulas and with the characteristic hematinic action have been isolated and designated: B12a, hydroxocobalamin; B12b, aquacobalamin; B12c, nitritocobalamin; B12r, cob(II)alamin; B12s, cob(I)alamin; B12III, factors A and V1a (cobyric acid) and pseudovitamin B12. Vitamins B12a and B12b are known to be tautomeric compounds; B12b has been obtained from cultures of Streptomyces aureofaciens; B12c has been obtained from cultures of Streptomyces griseus and is distinguishable from B12 by differences in its absorption spectrum. The physiologically active vitamin B12 coenzymes are methylcobalamin and deoxyadenosinecobalamin. A deficiency of vitamin B12 is often associated with certain methylmalonic acidurias.
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