title: Assessment of a futile cycle involving reconversion of fructose 6-phosphate to fructose 1,6-bisphosphate during gluconeogenic growth of Escherichia coli.
abstract: In gluconeogenesis, fructose 6-phosphate is formed from fructose 1,6-bisphosphate, and if fructose 1,6-bisphosphate were reformed by the phosphofructokinase reaction there would be a "gluconeogenic futile cycle." We assessed the extent of this cycling in Escherichia coli growing on glycerol 3-phosphate, using a medium containing 32Pi. Fructose 1,6-bisphosphate coming from glycerol 3-phosphate should be unlabeled, but any coming from fructose 6-phosphate should contain label from the gamma-position of ATP. The amount of labeling of the 1-position of fructose 1,6-bisphosphate was only 2 to 10% of that of the gamma-position of ATP in a series of isogenic strains differing in phosphofructokinases (Pfk-1, Pfk-2, or Pfk-2). In control experiments with glucose 6-phosphate instead of glycerol 3-phosphate, the two positions were equally labeled. Thus, although the presence of Pfk-2 causes gluconeogenic impairment (Daldal et al., Eur. J. Biochem., 126:373-379, 1982), gluconeogenic futile cycling cannot be the reason.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism*; D005635:Fructosediphosphates / Q000378:metabolism*; D005636:Fructosephosphates / Q000378:metabolism*; D005943:Gluconeogenesis; D005994:Glycerophosphates / Q000378:metabolism; D006598:Hexosediphosphates / Q000378:metabolism*; D010732:Phosphofructokinase-1 / Q000378:metabolism
chemical_list: D005635:Fructosediphosphates; D005636:Fructosephosphates; D005994:Glycerophosphates; D006598:Hexosediphosphates; C027618:fructose-6-phosphate; D000255:Adenosine Triphosphate; C029620:alpha-glycerophosphoric acid; D010732:Phosphofructokinase-1; C029063:fructose-1,6-diphosphate