IUBMB Enzyme Nomenclature


Accepted name: aerobic 5,6-dimethylbenzimidazole synthase

Reaction: FMNH2 + O2 = 5,6-dimethylbenzimidazole + D-erythrose 4-phosphate + other product(s)

For diagram of reaction click here

Other name(s): BluB; flavin destructase

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, PDB, CAS registry number:


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 (2007) 449. [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]

5. Collins, H.F., Biedendieck, R., Leech, H.K., Gray, M., Escalante-Semerena, J.C., McLean, K.J., Munro, A.W., Rigby, S.E., Warren, M.J. and Lawrence, A.D. Bacillus megaterium has both a functional BluB protein required for DMB synthesis and a related flavoprotein that forms a stable radical species. PLoS One 8 (2013) e55708. [PMID: 23457476]

[EC created 2010 as EC, transferred 2014 to EC, modified 2019]

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