IUBMB Enzyme Nomenclature


Accepted name: adenosylcobinamide-GDP ribazoletransferase

Reaction: (1) adenosylcobinamide-GDP + α-ribazole = GMP + adenosylcobalamin
(2) adenosylcobinamide-GDP + α-ribazole 5'-phosphate = GMP + adenosylcobalamin 5'-phosphate

For diagram click here.

Other name(s): CobS; cobalamin synthase; cobalamin-5'-phosphate synthase; cobalamin (5'-phosphate) synthase

Systematic name: adenosylcobinamide-GDP:α-ribazole ribazoletransferase

Comments: In Salmonella typhimurium LT2, under anaerobic conditions, CobU (EC and EC, CobT (EC, CobC (EC and CobS (EC catalyse reactions in the nucleotide loop assembly pathway, which convert adenosylcobinamide (AdoCbi) into adenosylcobalamin (AdoCbl). CobT and CobC are involved in 5,6-dimethylbenzimidazole activation whereby 5,6-dimethylbenzimidazole is converted to its riboside, α-ribazole. The second branch of the nuclotide loop assembly pathway is the cobinamide activation branch where AdoCbi or adenosylcobinamide-phosphate is converted to the activated intermediate AdoCbi-GDP by the bifunctional enzyme Cob U. CobS catalyses the final step in adenosylcobalamin biosynthesis, which is the condensation of AdoCbi-GDP with α-ribazole to yield adenosylcobalamin.

Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, CAS registry number: 137672-85-6


1. Maggio-Hall, L.A. and Escalante-Semerena, J.C. In vitro synthesis of the nucleotide loop of cobalamin by Salmonella typhimurium enzymes. Proc. Natl. Acad. Sci. USA 96 (1999) 11798-11803. [PMID: 10518530]

2. Warren, M.J., Raux, E., Schubert, H.L. and Escalante-Semerena, J.C. The biosynthesis of adenosylcobalamin (vitamin B12). Nat. Prod. Rep. 19 (2002) 390-412. [PMID: 12195810]

3. Cameron, B., Blanche, F., Rouyez, M.C., Bisch, D., Famechon, A., Couder, M., Cauchois, L., Thibaut, D., Debussche, L. and Crouzet, J. Genetic analysis, nucleotide sequence, and products of two Pseudomonas denitrificans cob genes encoding nicotinate-nucleotide: dimethylbenzimidazole phosphoribosyltransferase and cobalamin (5'-phosphate) synthase. J. Bacteriol. 173 (1991) 6066-6073. [PMID: 1917841]

[EC created 2004]

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