title: Novel phosphoenolpyruvate-dependent futile cycle in Streptococcus lactis: 2-deoxy-D-glucose uncouples energy production from growth.
abstract: The addition of 2-deoxy-D-glucose to cultures of Streptococcus lactis 133 that were growing exponentially on sucrose or lactose reduced the growth rate by ca. 95%. Inhibition did not occur with glucose or mannose as the growth sugar. The reduction in growth rate was concomitant with rapid accumulation of the analog in phosphorylated form (2-deoxy-D-glucose 6-phosphate) via the phosphoenolpyruvate-dependent mannose:phosphotransferase system. Within 5 min the intracellular 2-deoxy-D-glucose 6-phosphate concentration reached a steady-state level of greater than 100 mM. After maximum accumulation of the sugar phosphate, the rate of sucrose metabolism (glycolysis) decreased by only 30%, but the cells were depleted of fructose-1,6-diphosphate. The addition of glucose to 2-deoxy-D-glucose 6-phosphate preloaded cells caused expulsion of 2-deoxy-D-glucose and a resumption of normal growth. S. lactis 133 contained an intracellular Mg2+-dependent, fluoride-sensitive phosphatase which hydrolyzed 2-deoxy-D-glucose 6-phosphate (and glucose 6-phosphate) to free sugar and inorganic phosphate. Because of continued dephosphorylation and efflux of the non-metabolizable analog, the maintenance of the intracellular 2-deoxy-D-glucose 6-phosphate pool during growth stasis was dependent upon continued glycolysis. This steady-state condition represented a dynamic equilibrium of: (i) phosphoenolpyruvate-dependent accumulation of 2-deoxy-D-glucose 6-phosphate, (ii) intracellular dephosphorylation, and (iii) efflux of free 2-deoxy-D-glucose. This sequence of events constitutes a futile cycle which promotes the dissipation of phosphoenolpyruvate. We conclude that 2-deoxy-D-glucose functions as an uncoupler by dissociating energy production from growth in S. lactis 133.
mesh_terms: D003837:Deoxy Sugars / Q000494:pharmacology*; D003847:Deoxyglucose / Q000378:metabolism / Q000494:pharmacology*; D004734:Energy Metabolism / Q000187:drug effects*; D019298:Glucose-6-Phosphate / Q000031:analogs & derivatives*; D005958:Glucosephosphates / Q000378:metabolism; D006019:Glycolysis; D013294:Lactococcus lactis / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D008358:Mannose / Q000378:metabolism; D010728:Phosphoenolpyruvate / Q000378:metabolism*; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism
chemical_list: D003837:Deoxy Sugars; D005958:Glucosephosphates; C015785:2-deoxyglucose-6-phosphate; D019298:Glucose-6-Phosphate; D013395:Sucrose; D010728:Phosphoenolpyruvate; D003847:Deoxyglucose; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System; D010744:Phosphoric Monoester Hydrolases; D008358:Mannose