EC - Adenosylcobinamide-GDP ribazoletransferase

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IntEnz Enzyme Nomenclature


Accepted name:
adenosylcobinamide-GDP ribazoletransferase
Other names:
cobalamin synthase
cobalamin-5'-phosphate synthase
cobalamin (5'-phosphate) synthase
Systematic name:
adenosylcobinamide-GDP:α-ribazole ribazoletransferase



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 into its riboside, α-ribazole. The second branch of the nucleotide loop assembly pathway is the cobinamide activation branch where AdoCbi or adenosylcobinamide-phosphate is converted into 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

Enzymes and pathways: NC-IUBMB , BRENDA , DIAGRAM , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Structural data: CSA , EC2PDB
Gene Ontology: GO:0051073
CAS Registry Number: 137672-85-6
UniProtKB/Swiss-Prot: (247) [show] [UniProt]


  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 : 11798-11803 (1999). [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 : 390-412 (2002). [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 : 6066-6073 (1991). [PMID: 1917841]

[EC created 2004]