الوصف

The four vitamers of B*2 are all deeply red-colored crystals and water solutions, due to the color of the cobalt-corrin complex.

Cyanocobalamin is one form of B*2 because it can be metabolized in the body to an active coenzyme form. The cyanocobalamin form of B*2 does not occur in nature normally, but is a byproduct of the fact that other forms of B*2 are avid binders of cyanide (CN) which they pick up in the process of activated charcoal purification of the vitamin after it is made by bacteria in the commercial process. Since the cyanocobalamin form of B*2 is easy to crystallize and is not sensitive to air-oxidation, it is typically used as a form of B*2 for food additives and in many common multivitamins. Pure cyanocobalamin possesses the deep pink color associated with most octahedral cobalt(II) complexes and the crystals are well formed and easily grown up to millimeter size.

Hydroxocobalaminis another vitamer of B*2 commonly encountered in pharmacology, but is not normally present in the human body. Hydroxocobalamin is sometimes denoted B*2a. This is the form of B*2 produced by bacteria, and which is converted to cyanocobalmin in the commercial charcoal filtration step of production. Hydroxocobalamin has an avid affinity for cyanide ions and has been used as an antidote to cyanide poisoning. It is supplied typically in water solution for injection. Hydroxocobalamin is thought to be converted to the active enzymic forms of B*2 more easily than cyanocobalamin, and since it is little more expensive than cyanocobalamin, and has longer retention times in the body, has been used for vitamin replacement in situations where added reassurance of activity is desired. Intramuscular administration of hydroxocobalamin is also the preferred treatment for pediatric patients with intrinsic cobalamin metabolic diseases, for vitamin B*2 deficient patients with tobacco amblyopia (which is thought to perhaps have a component of cyanide poisoning from cyanide in cigarette smoke); and for treatment of patients with pernicious anemia who have optic neuropathy.

Adenosylcobalamin (adoB*2)and methylcobalamin (MeB*2) are the two enzymatically active cofactor forms of B*2 that naturally occur in the body. Most of the body's reserves are stored as adoB*2 in the liver. These are converted to the other methylcobalamin form as needed.