Cobamide, coenzymes derived from

In the biosynthesis of the coenzymes derived from vitamin B 2. cobalt is reduced from a trivalent to a monovalent state before the organic anionic ligands are attached to the suuctuie. The two types of cobamide that participate as coenzymes in human metabolism are the adcnosylcobamides and the nKthylcobamides. These coenzymes perform vital functions in methylinalonate-succinate isomerization and in methylation of homocy.steine to methionine. 

The catalysis of the transfer of a methyl group is an important role of enzyme-bound vitamin B12 derivatives in human, animal, and bacterial metabolism. The known enzyme-controlled methyl group-transfer reactions are key steps in the cobamide-dependent methylations of homocysteine to methionine, in the metabolic formation of methane from other Ci-compounds in methanogenic bacteria, and in the fixation of carbon dioxide via the acetyl coenzyme A pathway of some bacterial autotrophs (Figure 10). ... 

Cobalt is an essential element for bacteria, algae and ruminant mammals. For other organisms, including monogastric animals, cobalt is essential, in the form of the essential compound vitamin Bj2 (cobalamin). Rumen microflora of ruminants synthesises cobal-amin from cobalt in the diet. Derivatives of vitamin Bj2 cobamides are cofactors of some enzymes, for example of methyhnalonyl coenzyme A mutase, glutamate mutase and methionin synthetase. 

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