The Enzyme Database

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Accepted name: 5-hydroxybenzimidazole synthase
Reaction: 5-amino-1-(5-phospho-β-D-ribosyl)imidazole + S-adenosyl-L-methionine + reduced acceptor = 5-hydroxybenzimidazole + 5′-deoxyadenosine + L-methionine + formate + NH3 + phosphate + oxidized acceptor
For diagram of 5-hydroxybenzimidazole biosynthesis, click here
Other name(s): bzaF (gene name); HBI synthase
Systematic name: 5-amino-1-(5-phospho-β-D-ribosyl)imidazole formate-lyase (5-hydroxybenzimidazole-forming)
Comments: The enzyme, purified from bacteria, is part of the anaerobic pathway for cobalamin biosynthesis. It binds a [4Fe-4S] cluster that is coordinated by 3 cysteines and an exchangeable S-adenosyl-L-methionine molecule. The first stage of catalysis is reduction of the S-adenosyl-L-methionine to produce L-methionine and a 5′-deoxyadenosin-5′-yl radical that is crucial for the conversion of the substrate.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
1.  Mehta, A.P., Abdelwahed, S.H., Fenwick, M.K., Hazra, A.B., Taga, M.E., Zhang, Y., Ealick, S.E. and Begley, T.P. Anaerobic 5-hydroxybenzimidazole formation from aminoimidazole ribotide: an unanticipated intersection of thiamin and vitamin B12 biosynthesis. J. Am. Chem. Soc. 137 (2015) 10444–10447. [DOI] [PMID: 26237670]
2.  Hazra, A.B., Han, A.W., Mehta, A.P., Mok, K.C., Osadchiy, V., Begley, T.P. and Taga, M.E. Anaerobic biosynthesis of the lower ligand of vitamin B12. Proc. Natl. Acad. Sci. USA 112 (2015) 10792–10797. [DOI] [PMID: 26246619]
[EC created 2017]

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