Vitamin B12/ja: Difference between revisions

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==Synthesis==

===Biosynthesis===

{{Main|Cobalamin biosynthesis}}

Vitamin B₁₂ is derived from a [[tetrapyrrole|tetrapyrrolic structural framework]] created by the enzymes [[Porphobilinogen deaminase|deaminase]] and [[uroporphyrinogen III synthase|cosynthetase]] which transform [[aminolevulinic acid]] via [[porphobilinogen]] and [[hydroxymethylbilane]] to [[uroporphyrinogen III]]. The latter is the first [[macrocycle|macrocyclic]] intermediate common to [[heme]], [[chlorophyll]], [[siroheme]] and B₁₂ itself. Later steps, especially the incorporation of the additional methyl groups of its structure, were investigated using ¹³C [[isotopic labelling|methyl-labelled]] [[S-adenosyl methionine]]. It was not until a [[genetic engineering|genetically engineered]] strain of ''[[Pseudomonas denitrificans]]'' was used, in which eight of the genes involved in the biosynthesis of the vitamin had been [[gene expression|overexpressed]], that the complete sequence of [[methylation]] and other steps could be determined, thus fully establishing all the intermediates in the pathway.