vitamin B12 biosynthesis in bacteria

Vitamin B12 is a complex molecule synthesised solely by bacteria. The chemistry of B12 proved to be a difficult task and during the elucidation of its chemistry and biochemistry four Nobel prizes have been won. One fragment of the vitamin has defied understanding until recently ( Ealick and Begely Nature 446, 22nd March 2007 pp 387-8 ) . This is the dimethylbenzimidazole ligand. ( DMB). reaction
There are several structurally related compounds of B12, only two have major recognised biological activity, methyl cobalamin ( a methyl donor in methionine biosynthesis ) and 5-deoxyadenosylcobalamin ( Ado B12) which is the source of the adenosyl radical, important in catalysing reactions with the removal of a hydrogen atom from a compound.
Ado B12 is the only organometallic compound used by living systems. The biosynthesis of which requires the destruction of vitamin B2., riboflavin. The enzyme is a flavin destructase ( BluB) , a reaction requiring oxygen. The enzyme catalyses the conversion of reduced flavin mononucleotide ( FMN ) to dimethylbenzimidazole ligand. ( DMB). The cannibalisation of one vitamin to create another, an interlinking system.
The writers of this fascinating article are surprised that this happens. But biochemistry is about the destruction of one chemical to form another. The fact that a vitamin is lost surely underlines why we have to continuously to stock up with more of the vitamin. .

Martin Eastwood
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