The Enzyme Database

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Accepted name: 5,6-dimethylbenzimidazole synthase
Reaction: FMNH2 + O2 = 5,6-dimethylbenzimidazole + D-erythrose 4-phosphate + other product(s)
For diagram of FAD biosynthesis, click here
Other name(s): BluB
Systematic name: FMNH2 oxidoreductase (5,6-dimethylbenzimidazole-forming)
Comments: The enzyme catalyses a complex oxygen-dependent conversion of reduced flavin mononucleotide to form 5,6-dimethylbenzimidazole, the lower ligand of vitamin B12. This conversion involves many sequential steps in two distinct stages, and an alloxan intermediate that acts as a proton donor, a proton acceptor, and a hydride acceptor [4]. The C-2 of 5,6-dimethylbenzimidazole is derived from C-1′ of the ribityl group of FMNH2 and 2-H from the ribityl 1′-pro-S hydrogen. While D-erythrose 4-phosphate has been shown to be one of the byproducts, the nature of the other product(s) has not been verified yet.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
1.  Gray, M.J. and Escalante-Semerena, J.C. Single-enzyme conversion of FMNH2 to 5,6-dimethylbenzimidazole, the lower ligand of B12. Proc. Natl. Acad. Sci. USA 104 (2007) 2921–2926. [PMID: 17301238]
2.  Ealick, S.E. and Begley, T.P. Biochemistry: molecular cannibalism. Nature 446 (2007) 387–388. [PMID: 17377573]
3.  Taga, M.E., Larsen, N.A., Howard-Jones, A.R., Walsh, C.T. and Walker, G.C. BluB cannibalizes flavin to form the lower ligand of vitamin B12. Nature 446:449 (2007). [PMID: 17377583]
4.  Wang, X.L. and Quan, J.M. Intermediate-assisted multifunctional catalysis in the conversion of flavin to 5,6-dimethylbenzimidazole by BluB: a density functional theory study. J. Am. Chem. Soc. 133 (2011) 4079–4091. [PMID: 21344938]
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