Vitamin B12 (hydroxocobalamin, hydroxycobalamin or B12a) is a water-soluble vitamin synthesised by intestinal flora that forms a cobalt-based coenzyme that is required for two vital cellular reactions, namely the production of methionine (an amino acid) and the metabolism of odd-number carbon atom fatty acids.
Deficiency leads to cell membrane dysfunction as it is incorporated with abnormal fatty acids, in which the CNS is particularly susceptible.
Deficiency due to reduced absorption is known as pernicious anaemia where there is failure of absorption of intrinsic factor (IF) in the distal ileum. IF is made by the parietal cells in the stomach and bind to cobalamin. The IF-cobalamin complex is subsequently absorbed by specialised receptors in the epithelial cells of the distal ileum. Chronic pathology of the terminal ileum (such as Crohn disease) and distal ileum surgical resections can lead to reduced absorption of the complex and hence lead to pernicious anaemia.
Due to its involvement with folate in the synthesis of amino acids and nucleic bases, B12 deficiency can precipitate folate deficiency.
- 1. Pamela C. Champe, Richard A. Harvey (Ph. D.), Denise R. Ferrier. Biochemistry. ISBN: 0781769604
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