|Superclasses:||Reactions Classified By Conversion Type → Simple Reactions → Chemical Reactions|
|Reactions Classified By Substrate → Small-Molecule Reactions|
EC Number: 18.104.22.168
In Pathway: adenosylcobalamin salvage from cobinamide I
Note that this reaction equation differs from the official Enzyme Commission reaction equations for this EC number.
The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.
Most BioCyc compounds have been protonated to a reference pH value of 7.3, and some reactions have been computationally balanced for hydrogen by adding free protons. Please see the PGDB Concepts Guide for more information.
Mass balance status: Balanced.
Enzyme Commission Primary Name: adenosylcobinamide kinase
Enzyme Commission Synonyms: CobU, adenosylcobinamide kinase/adenosylcobinamide-phosphate guanylyltransferase, AdoCbi kinase/AdoCbi-phosphate guanylyltransferase
This reaction is part of cobalamin biosynthesis.
Enzyme Commission Summary:
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) 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 nucleotide loop assembly pathway is the cobinamide (Cbi) activation branch where AdoCbi or adenosylcobinamide-phosphate is converted to the activated intermediate AdoCbi-GDP by Cob U. The final step in adenosylcobalamin biosynthesis is the condensation of AdoCbi-GDP with α-ribazole, which is catalysed by EC 18.104.22.168, adenosylcobinamide-GDP ribazoletransferase (CobS), to yield adenosylcobalamin. CobU is a bifunctional enzyme that has both kinase (EC 22.214.171.124) and guanylyltransferase (EC 126.96.36.199, adenosylcobinamide-phosphate guanylyltransferase) 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 [Thomas00a].
OToole95: O'Toole GA, Escalante-Semerena JC (1995). "Purification and characterization of the bifunctional CobU enzyme of Salmonella typhimurium LT2. Evidence for a CobU-GMP intermediate." J Biol Chem 270(40);23560-9. PMID: 7559521
Thomas00a: Thomas MG, Thompson TB, Rayment I, Escalante-Semerena JC (2000). "Analysis of the adenosylcobinamide kinase/adenosylcobinamide-phosphate guanylyltransferase (CobU) enzyme of Salmonella typhimurium LT2. Identification of residue His-46 as the site of guanylylation." J Biol Chem 275(36);27576-86. PMID: 10869342
Thompson98a: Thompson TB, Thomas MG, Escalante-Semerena JC, Rayment I (1998). "Three-dimensional structure of adenosylcobinamide kinase/adenosylcobinamide phosphate guanylyltransferase from Salmonella typhimurium determined to 2.3 A resolution,." Biochemistry 37(21);7686-95. PMID: 9601028
Thompson99b: Thompson TB, Thomas MG, Escalante-Semerena JC, Rayment I (1999). "Three-dimensional structure of adenosylcobinamide kinase/adenosylcobinamide phosphate guanylyltransferase (CobU) complexed with GMP: evidence for a substrate-induced transferase active site." Biochemistry 38(40);12995-3005. PMID: 10529169
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