title: Thiamine diphosphate adenylyl transferase from E. coli: functional characterization of the enzyme synthesizing adenosine thiamine triphosphate.
abstract: BACKGROUND
  We have recently identified a new thiamine derivative, adenosine thiamine triphosphate (AThTP), in E. coli. In intact bacteria, this nucleotide is synthesized only in the absence of a metabolizable carbon source and quickly disappears as soon as the cells receive a carbon source such as glucose. Thus, we hypothesized that AThTP may be a signal produced in response to carbon starvation.
  
  
  RESULTS
  Here we show that, in bacterial extracts, the biosynthesis of AThTP is carried out from thiamine diphosphate (ThDP) and ADP or ATP by a soluble high molecular mass nucleotidyl transferase. We partially purified this enzyme and characterized some of its functional properties. The enzyme activity had an absolute requirement for divalent metal ions, such as Mn2+ or Mg2+, as well as for a heat-stable soluble activator present in bacterial extracts. The enzyme has a pH optimum of 6.5-7.0 and a high Km for ThDP (5 mM), suggesting that, in vivo, the rate of AThTP synthesis is proportional to the free ThDP concentration. When ADP was used as the variable substrate at a fixed ThDP concentration, a sigmoid curve was obtained, with a Hill coefficient of 2.1 and an S0.5 value of 0.08 mM. The specificity of the AThTP synthesizing enzyme with respect to nucleotide substrate is restricted to ATP/ADP, and only ThDP can serve as the second substrate of the reaction. We tentatively named this enzyme ThDP adenylyl transferase (EC 2.7.7.65).
  
  
  CONCLUSIONS
  This is the first demonstration of an enzyme activity transferring a nucleotidyl group on thiamine diphosphate to produce AThTP. The existence of a mechanism for the enzymatic synthesis of this compound is in agreement with the hypothesis of a non-cofactor role for thiamine derivatives in living cells.
authors: Center for Cellular and Molecular Neurobiology, University of Liège, Liège, Belgium. a_makarchikov@yahoo.com <a_makarchikov@yahoo.com>
authors: Alexander F
authors: AF
authors: Makarchikov
authors: Alain
authors: A
authors: Brans
authors: Lucien
authors: L
authors: Bettendorff
mesh_terms: D000244:Adenosine Diphosphate / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000096:biosynthesis* / Q000737:chemistry; D002852:Chromatography, Ion Exchange; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000302:isolation & purification / Q000378:metabolism*; D008274:Magnesium / Q000737:chemistry; D008345:Manganese / Q000737:chemistry; D008970:Molecular Weight; D009713:Nucleotidyltransferases / Q000302:isolation & purification / Q000378:metabolism*; D013379:Substrate Specificity; D013838:Thiamine Triphosphate / Q000096:biosynthesis* / Q000737:chemistry
chemical_list: D029968:Escherichia coli Proteins; C519454:adenosine thiamine triphosphate; D013838:Thiamine Triphosphate; D008345:Manganese; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D009713:Nucleotidyltransferases; C524661:thiamine diphosphate adenylyl transferase, E coli; D008274:Magnesium
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