Cobalt is essential to the metabolism of allanimals. It is a key constituent ofcobalamin, also known as vitamin B12, the primary biological reservoir of cobalt as anultratrace element.[1][2]Bacteria in the stomachs ofruminant animals convert cobalt salts into vitamin B12, a compound which can only be produced by bacteria orarchaea. A minimal presence of cobalt in soils therefore markedly improves the health ofgrazing animals, and an uptake of 0.20 mg/kg a day is recommended because they have no other source of vitamin B12.[3]
Proteins based on cobalamin usecorrin to hold the cobalt. Coenzyme B12 features a reactive C-Co bond that participates in the reactions.[4] In humans, B12 has two types ofalkylligand:methyl and adenosyl.MeB12 promotes methyl (−CH3) group transfers. The adenosyl version of B12 catalyzes rearrangements in which a hydrogen atom is directly transferred between two adjacent atoms with concomitant exchange of the second substituent, X, which may be a carbon atom with substituents, an oxygen atom of an alcohol, or an amine.Methylmalonyl coenzyme A mutase (MUT) convertsMMl-CoA toSu-CoA, an important step in the extraction of energy from proteins and fats.[5]
Although far less common than othermetalloproteins (e.g. those of zinc and iron), other cobaltoproteins are known besides B12. These proteins includemethionine aminopeptidase 2, an enzyme that occurs in humans and other mammals that does not use the corrin ring of B12, but binds cobalt directly. Another non-corrin cobalt enzyme isnitrile hydratase, an enzyme in bacteria that metabolizesnitriles.[6]
In humans, consumption of cobalt-containing vitamin B12 meets all needs for cobalt. For cattle and sheep, which meet vitamin B12 needs via synthesis by resident bacteria in the rumen, there is a function for inorganic cobalt. In the early 20th century, during the development of farming on theNorth Island Volcanic Plateau of New Zealand, cattle suffered from what was termed "bush sickness". It was discovered that the volcanic soils lacked the cobalt salts essential for the cattle food chain.[7][8] The "coast disease" of sheep in theNinety Mile Desert of theSoutheast ofSouth Australia in the 1930s was found to originate in nutritional deficiencies of trace elements cobalt and copper. The cobalt deficiency was overcome by the development of "cobalt bullets", dense pellets of cobalt oxide mixed with clay given orally for lodging in the animal'srumen.[clarification needed][9][8][10]
