ENZYME entry: EC 18.104.22.168
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|AdoCbi kinase/AdoCbi-phosphate guanylyltransferase.|
|GTP + adenosylcobinamide phosphate <=> diphosphate + adenosylcobinamide-GDP|
- In Salmonella typhimurium LT2, under anaerobic conditions, CobU
(EC 22.214.171.124 and EC 126.96.36.199), CobT (EC 188.8.131.52),
CobC (EC 184.108.40.206) and CobS (EC 220.127.116.11) catalyze 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,
- The second branch of the nuclotide loop assembly pathway is the
cobinamide (Cbi) activation branch where AdoCbi or
adenosylcobinamide-phosphate is converted to the activated
intermediate AdoCbi-GDP by the bifunctional enzyme CobU.
- The final step in adenosylcobalamin biosynthesis is the condensation
of AdoCbi-GDP with alpha-ribazole, which is catalyzed by CobS
(EC 18.104.22.168), to yield adenosylcobalamin.
- CobU is a bifunctional enzyme that has both kinase (EC 22.214.171.124) and
guanylyltransferase (EC 126.96.36.199) activities.
- However, both activities are not required at all times.
- The kinase activity has been proposed to function only when
S.typhimurium is assimilating cobinamide whereas the
guanylyltransferase activity is required for both assimilation of
exogenous cobinamide and for de novo synthesis of adenosylcobalamin.
- The guanylyltransferase reaction is a two-stage reaction with
formation of a CobU-GMP intermediate.
|PRIAM enzyme-specific profiles||188.8.131.52|
|KEGG Ligand Database for Enzyme Nomenclature||184.108.40.206|
|IUBMB Enzyme Nomenclature||220.127.116.11|
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