Cobalamin (vitamin B12)
coenzyme for methionine synthetase ( important in metabolism of folic acid), methylmalonyl CoA mutase and leucine aminomutase .
Deficiency leads to pernicious anaemia when immature red blood cells are released into the bloodstream, and there is degeneration of the spinal cord. The anaemia is the same as seen in folate deficiency, and is due to impairment of folate metabolism. There is also urinary excretion of methylmalonic acid.
Absorption of vitamin B12 requires intrinsic factor, a protein secreted in the gastric juice. Failure of absorption, rather than dietary deficiency, is the main cause of pernicious anaemia. However, B12 is found only in animal foods so strict vegetarians are at risk.