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 188.8.131.52 and EC 184.108.40.206), CobT (EC 220.127.116.11), CobC (EC 18.104.22.168) and CobS (EC 22.214.171.124) 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
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