http://www.pnas.org/cgi/content/extract/103/13/4799

Ever since Dorothy Hodgkin solved the structure of vitamin B12 some 50 years ago, researchers have been puzzling over how this amazing molecular jigsaw is pieced together. In essence, vitamin B12 is a modified tetrapyrrole (corrinoid ring) to which is attached either an upper adenosyl or methyl group and a lower base, usually dimethylbenzimidazole (DMB) (Fig. 1). Although significant success has been achieved toward an understanding of the construction of the corrin ring component of the coenzyme, there has been a paucity of information concerning the biosynthesis of DMB. In a recent issue of PNAS, Campbell et al. (1) identified an enzyme that appears to play a key role in the transformation of flavin into DMB.