In?Salmonella typhimurium?LT2, under anaerobic conditions, CobU (EC?2.7.7.62?and EC?2.7.1.156), CobT (EC?2.4.2.21), CobC (EC?3.1.3.73) and CobS (EC?2.7.8.26) 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, ¦Á-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 ¦Á-ribazole to yield adenosylcobalamin.
