title: Intracellular xylitol-phosphate hydrolysis and efflux of xylitol in Streptococcus sobrinus.
abstract: The parental strain Streptococcus sobrinus (Streptococcus mutans ATCC 27352), which is known to transport, phosphorylate and accumulate xylitol intracellularly as nonmetabolizable xylitol-phosphate (xylitol-sensitive (XS) strain) and its xylitol-resistant (XR) spontaneous mutant were used to further investigate the inhibitory action of xylitol on oral streptococci. Fructose-grown XR cells did not accumulate xylitol-phosphate, indicating that the inducible fructose PTS is incapable of transporting the pentitol. The intracellularly accumulated pentitol-phosphate by the XS cells did not prevent the subsequent uptake and degradation of glucose or fructose, despite a drop in the PEP pool and a 50% inhibition of the glucose but not the fructose catabolism. Intracellular dephosphorylation of the pentitol-phosphate and release of xylitol in the extracellular medium resulted in a rapid decrease of the intracellular level of this nonmetabolizable product. A Mg(++)- or Mn(++)-independent sugar-phosphate hydrolysing activity capable of splitting xylitol-phosphate was demonstrated in both XS and XR strains. Preincubation in the presence of N1-ethylmaleimide (NEM) and xylitol or NEM and fructose resulted in the subsequent inhibition of both xylitol uptake and efflux. The efflux kinetic at various temperatures is compatible with a facilitated diffusion by the phosphotransferase system EIIfru without, however, excluding the existence of an additional exit route, but it excludes a simple diffusion exit process. The results are consistent with the existence of a xylitol futile cycle contributing to the growth inhibition of S. sobrinus by the pentitol without excluding a toxic effect of xylitol-phosphate. Discrepancies in the literature on the action of xylitol on S. mutans could be explained in the light of the evidence presented.
authors.affiliation: Ecole de Médecine Dentaire, Université Laval, Ste-Foy, Québec, Canada.
authors.forename: L
authors.initials: L
authors.lastname: Trahan
authors.forename: S
authors.initials: S
authors.lastname: Néron
authors.forename: M
authors.initials: M
authors.lastname: Bareil
mesh_terms: D003773:Dental Plaque / Q000382:microbiology; D005632:Fructose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006868:Hydrolysis; D009943:Organophosphorus Compounds / Q000494:pharmacology; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D010770:Phosphotransferases / Q000378:metabolism; D016986:Streptococcus sobrinus / Q000187:drug effects* / Q000378:metabolism*; D015219:Substrate Cycling; D014993:Xylitol / Q000378:metabolism*
chemical_list: D009943:Organophosphorus Compounds; D005632:Fructose; D010770:Phosphotransferases; D010744:Phosphoric Monoester Hydrolases; D005947:Glucose; D014993:Xylitol