Cyanocobalamin

Cyanocobalamin is an especially common "vitamer" (that is, member of a family of vitamins, all of which have some particular nutritional activity in preventing some vitamin deficiency disease). In the case of the B-12 vitamin family (see Vitamin B-12), cyanocobalamin is the most famous of the B-12 vitamers, because it is chemically the most air-stable, and it is the easiest to crystallize and therefore easiest to purify after it is produced by bacterial fermentation. The cyanide is added to the molecule by activated charcoal columns in purification. Thus, the use of this form of B-12 is the most wide-spread. ^[1]

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This latter fact has caused some people (usually from reading labels on packages and vitamin supplements, in which vitamin B-12 is almost always listed last, since ingredients by law are listed in order of weight %), to infer that the "correct" chemical name of vitamin B-12 actually IS cyanocobalamin. In fact, "vitamin B-12" is the name for a whole class of chemicals with B-12 activity, and "cyanocobalamin" is only one of these. Cyanocobalamin usually does not even occur in nature, and cyanocobalamin is not one of the forms of this vitamin which is directly used in the human body (or that of any other animal). However, animals and humans can convert it to active (cofactor) forms of the vitamin, such as methylcobalamin. ^[2]

References

1. ^ http://www.ajcn.org/cgi/reprint/48/3/852.pdf. Accessed Dec. 3, 2007. See page 853 for the discussion that cyanocobalamin is not the natural form, but was accidentally discovered in purification of B-12 from activated charcoal columns.
2. ^ op. cit.