The Vitamin B12 molecule in 3-D

The Vitamin B12 (cyanocobalamin) molecule - rotatable in 3 dimensions

Vitamin B12 is quite a complex molecule, and uniquely it contains the metal cobalt. There are several of these cobalamin compounds, but none are synthesised by plants or animals - they must be originally obtained from bacteria. Ruminant animals are quite important here as their gut contains many bacteria and having absorbed some of these products, their meat is a source of vitamin B12. In fact vitamin B12 in the diet is bound by various proteins and within the digestive system a number of molecules are produced to assist in its absorption, which sometimes cause problems. The possible contribution by bacteria in the human gut is somewhat debatable.

It is involved in synthesis and repair of DNA, important in cell division, and also in fatty acid synthesis and energy metabolism.

In the middle of the molecule is a corrin ring (rather like a porphyrin ring) composed of 4 pyrrole subunits, with amide groups projecting out sideways. From another one of these, a section like a nucleotide (consisting of phosphate, ribose and a dimethylbenzimidazole group) extends underneath the ring. The cobalt atom is held between 5 nitrogen atoms. In cyanocobalamin, a cyanide group is attached here. In the liver this is converted to other forms and then the active form adenosylcobalamin.

Label/ Unlabel atoms